if you mean within the same B3D file as the exterior, just reduce by at least 0.03. For example if the train's width is -1.30 & 1.30, then it would be -1.28 & 1.28, respectively. Then just make the door areas blue, and where the window glass would be, also blue.
For the train ends, copy and paste the coordinates for the car ends, then just use the same coordinates for the car ends. If it ends at -18.50, use -18.50, making it flat. Adjust the end where the cab would normally be, and move that part of the code where the wall of the cab would be, until the cab window is no longer visible.
Replace the interior provisions with the proper interior textures.
Here's just an example of what im talking about:
;-------------
;Front end
;-------------
[MeshBuilder]
Vertex -1.31, 3.10, -15.32
Vertex -0.40, 3.10, -15.67
Vertex -0.40, 0.0, -15.67
Vertex -1.31, 0.0, -15.32
Vertex -0.40, 3.10, -15.32
Vertex 0.40, 3.10, -15.32
Vertex 0.40, 0.0, -15.32
Vertex -0.40, 0.0, -15.32
Vertex 0.40, 3.10, -15.67
Vertex 1.31, 3.10, -15.32
Vertex 1.31, 0.0, -15.32
Vertex 0.40, 0.0, -15.67
vertex 1.31, 3.1, -15.32
vertex 0.40, 3.1, -15.67
vertex -0.40, 3.1, -15.67
vertex -1.31, 3.1, -15.32
vertex -0.40, 3.1, -15.32
vertex 0.40, 3.1, -15.32
Face2 0,1,2,3
Face 4,5,6,7
Face2 8,9,10,11
Face2 12,13,14,15,16,17
[Texture]
Load R15F.png
Coordinates 0, 0.00, .125
Coordinates 1, 0.34, .125
Coordinates 2, 0.34, 1
Coordinates 3, 0.00, 1
Coordinates 4, 0.35, .125
Coordinates 5, 0.66, .125
Coordinates 6, 0.66, 1
Coordinates 7, 0.35, 1
Coordinates 8, 0.67, .125
Coordinates 9, 1.00, .125
Coordinates 10, 1.00, 1
Coordinates 11, 0.67, 1
Coordinates 12, 1.00, .125
Coordinates 13, 0.67, .125
Coordinates 14, 0.35, .125
Coordinates 15, 0.00, .125
Coordinates 16, 0.35, 0
Coordinates 17, 0.67, 0
Transparent 0, 0, 255
[Meshbuilder]
Vertex -0.40, 3.64, -15.31
Vertex -0.40, 3.64, -15.67
Vertex -0.40, -0.15, -15.67
Vertex -0.40, -0.15, -15.31
Vertex 0.40, 3.64, -15.31
Vertex 0.40, 3.64, -15.67
Vertex 0.40, -0.15, -15.67
Vertex 0.40, -0.15, -15.31
Face2 0,1,2,3
Face2 4,5,6,7
[Texture]
Load R15FSide.png
Coordinates 0,1,0
Coordinates 1,0,0
Coordinates 2,0,1
Coordinates 3,1,1
Coordinates 4,1,0
Coordinates 5,0,0
Coordinates 6,0,1
Coordinates 7,1,1
Transparent 0,0,255
;Front End Interior
[MeshBuilder]
Vertex -1.31, 3.16, -14.47
Vertex -0.40, 3.16, -14.47
Vertex -0.40, -0.15, -14.47
Vertex -1.31, -0.15, -14.47
Vertex -0.40, 3.16, -15.31
Vertex 0.40, 3.16, -15.31
Vertex 0.40, -0.15, -15.31
Vertex -0.40, -0.15, -15.31
Vertex 0.40, 3.16, -15.31
Vertex 1.31, 3.16, -15.31
Vertex 1.31, -0.15, -15.31
Vertex 0.40, -0.15, -15.31
Face2 0,1,2,3
Face 7,6,5,4
Face2 8,9,10,11
[Texture]
Load R15FInt.png
Coordinates 0, 0.00, .125
Coordinates 1, 0.354, .125
Coordinates 2, 0.354, 1
Coordinates 3, 0.00, 1
Coordinates 4, 0.35, .125
Coordinates 5, 0.66, .125
Coordinates 6, 0.66, 1
Coordinates 7, 0.35, 1
Coordinates 8, 0.67, .125
Coordinates 9, 1.00, .125
Coordinates 10, 1.00, 1
Coordinates 11, 0.67, 1
Emissivecolor 255,255,255
Transparent 0, 0, 255
[MeshBuilder]
Vertex -1.27, 3.117, -14.47
Vertex -0.40, 3.117, -14.47
Vertex -0.40, 3.7, -14.47
Vertex -1.27, 3.7, -14.47
Vertex -0.40, 3.117, -15.32
Vertex 0.40, 3.117, -15.32
Vertex 0.40, 3.77, -15.32
Vertex -0.40, 3.77, -15.32
Vertex 0.40, 3.117, -15.32
Vertex 1.31, 3.117, -15.32
Vertex 1.31, 3.77, -15.32
Vertex 0.40, 3.77, -15.32
Face2 0,1,2,3
Face2 4,5,6,7
Face2 8,9,10,11
[Texture]
Load R15IntRound.png
Coordinates 0, 0.00, 0
Coordinates 1, 0.34, 0
Coordinates 2, 0.34, 1
Coordinates 3, 0.00, 1
Coordinates 4, 0.35, .125
Coordinates 5, 0.66, .125
Coordinates 6, 0.66, 1
Coordinates 7, 0.35, 1
Coordinates 8, 0.67, .125
Coordinates 9, 1.00, .125
Coordinates 10, 1.00, 1
Coordinates 11, 0.67, 1
Emissivecolor 255,255,255
Transparent 0, 0, 255
[Meshbuilder]
Vertex -0.40, 3.64, -15.31
Vertex -0.40, 3.64, -14.47
Vertex -0.40, -0.15, -14.47
Vertex -0.40, -0.15, -15.31
Face2 0,1,2,3
[Texture]
Load R15FIntCab.png
Coordinates 0,1,0
Coordinates 1,0,0
Coordinates 2,0,1
Coordinates 3,1,1
Transparent 0,0,255
Emissivecolor 255,255,255
;Front End Bulkhead
[MeshBuilder]
Vertex -1.31, 3.1, -15.32
Vertex -0.40, 3.1, -15.67
Vertex -0.40, 3.7, -15.67
Vertex -1.31, 3.7, -15.32
Vertex -0.40, 3.1, -15.67
Vertex 0.40, 3.1, -15.67
Vertex 0.40, 3.7, -15.67
Vertex -0.40, 3.7, -15.67
Vertex 0.40, 3.1, -15.67
Vertex 1.31, 3.1, -15.32
Vertex 1.31, 3.7, -15.32
Vertex 0.40, 3.7, -15.67
Face2 0,1,2,3
Face2 4,5,6,7
Face2 8,9,10,11
[Texture]
Load R15_bulk0.png
Coordinates 0, 0.00, .125
Coordinates 1, 0.34, .125
Coordinates 2, 0.34, 1
Coordinates 3, 0.00, 1
Coordinates 4, 0.35, .125
Coordinates 5, 0.66, .125
Coordinates 6, 0.66, 1
Coordinates 7, 0.35, 1
Coordinates 8, 0.67, .125
Coordinates 9, 1.00, .125
Coordinates 10, 1.00, 1
Coordinates 11, 0.67, 1
Transparent 0, 0, 255
;---------------
;Car's left side
;---------------
[MeshBuilder]
Vertex 1.31, 3.10, -15.32
Vertex 1.31, 3.10, -00.37
Vertex 1.31, 1.67, -00.37
Vertex 1.31, 1.67, -15.32
Vertex 1.31, 1.67, -15.32
Vertex 1.31, 1.67, -00.37
Vertex 1.31, 0.80, -00.37
Vertex 1.31, 0.80, -15.32
Vertex 0.80, 0.80, -15.22
Vertex 0.80, 0.80, -00.37
Vertex 0.80, 0.00, -00.37
Vertex 0.80, 0.00, -15.32
Face2 0,1,2,3
Face2 4,5,6,7
Face2 8,9,10,11
[Texture]
Load R15.png
Coordinates 0, 0, 0.150
Coordinates 1, 1, 0.150
Coordinates 2, 1, 0.55
Coordinates 3, 0, 0.55
Coordinates 4, 0, 0.551
Coordinates 5, 1, 0.551
Coordinates 6, 1, 0.78
Coordinates 7, 0, 0.78
Coordinates 8, 0, 0.781
Coordinates 9, 1, 0.781
Coordinates 10, 1, 1
Coordinates 11, 0, .98
Transparent 0, 0, 255
;Car's Left Side Interior
[MeshBuilder]
Vertex 0.50, 3.70, -15.67
Vertex 0.50, 3.70, -00.08
Vertex 1.27, 3.10, -00.37
Vertex 1.27, 3.10, -15.32
Vertex 1.27, 3.10, -15.32
Vertex 1.27, 3.10, -00.37
Vertex 1.27, 1.67, -00.37
Vertex 1.27, 1.67, -15.32
Vertex 1.27, 1.67, -15.32
Vertex 1.27, 1.67, -00.37
Vertex 1.27, 0.80, -00.37
Vertex 1.27, 0.80, -15.32
Vertex 0.80, 0.80, -15.22
Vertex 0.80, 0.80, -00.37
Vertex 0.80, 0.00, -00.37
Vertex 0.80, 0.00, -15.32
Face2 0,1,2,3
Face2 4,5,6,7
Face2 8,9,10,11
Face2 12,13,14,15
[Texture]
Load R15SInt.png
Coordinates 0, 0, 0
Coordinates 1, 1, 0
Coordinates 2, 1, 0.150
Coordinates 3, 0, 0.150
Coordinates 4, 0, 0.150
Coordinates 5, 1, 0.150
Coordinates 6, 1, 0.55
Coordinates 7, 0, 0.55
Coordinates 8, 0, 0.551
Coordinates 9, 1, 0.551
Coordinates 10, 1, 0.78
Coordinates 11, 0, 0.78
Coordinates 12, 0, 0.781
Coordinates 13, 1, 0.781
Coordinates 14, 1, 1
Coordinates 15, 0, .98
Emissivecolor 255,255,255
Transparent 0, 0, 255
;-------------
;Rear end
;-------------
[MeshBuilder]
Vertex 1.31, 3.10, -00.37
Vertex 0.40, 3.10, -00.07
Vertex 0.40, 0.0, -00.07
Vertex 1.31, 0.0, -00.37
Vertex 0.40, 3.10, -00.36
Vertex -0.40, 3.10, -00.36
Vertex -0.40, 0.0, -00.36
Vertex 0.40, 0.0, -00.36
Vertex -0.40, 3.10,-00.07
Vertex -1.31, 3.10,-00.37
Vertex -1.31, 0.0, -00.37
Vertex -0.40, 0.0, -00.07
vertex -1.31, 3.1, -00.32
vertex -0.40, 3.1, -00.07
vertex 0.40, 3.1, -00.07
vertex 1.31, 3.1, -00.32
vertex 0.40, 3.1, -00.32
vertex -0.40, 3.1, -00.32
Face2 0,1,2,3
Face 4,5,6,7
Face2 8,9,10,11
Face2 12,13,14,15,16,17
[Texture]
Load R15F.png
Coordinates 0, 0.00, .125
Coordinates 1, 0.34, .125
Coordinates 2, 0.34, 1
Coordinates 3, 0.00, 1
Coordinates 4, 0.35, .125
Coordinates 5, 0.66, .125
Coordinates 6, 0.66, 1
Coordinates 7, 0.35, 1
Coordinates 8, 0.67, .125
Coordinates 9, 1.00, .125
Coordinates 10, 1.00, 1
Coordinates 11, 0.67, 1
Coordinates 12, 1.00, .125
Coordinates 13, 0.67, .125
Coordinates 14, 0.35, .125
Coordinates 15, 0.00, .125
Coordinates 16, 0.35, 0
Coordinates 17, 0.67, 0
Transparent 0, 0, 255
[Meshbuilder]
Vertex -0.40, 3.64, -00.38
Vertex -0.40, 3.64, -00.07
Vertex -0.40, -0.15, -00.07
Vertex -0.40, -0.15, -00.38
Vertex 0.40, 3.64, -00.38
Vertex 0.40, 3.64, -00.07
Vertex 0.40, -0.15, -00.07
Vertex 0.40, -0.15, -00.38
Face2 0,1,2,3
Face2 4,5,6,7
[Texture]
Load R15FSide.png
Coordinates 0,1,0
Coordinates 1,0,0
Coordinates 2,0,1
Coordinates 3,1,1
Coordinates 4,1,0
Coordinates 5,0,0
Coordinates 6,0,1
Coordinates 7,1,1
Transparent 0,0,255
;Rear End Interior
[MeshBuilder]
Vertex 1.31, 3.16, -01.22
Vertex 0.40, 3.16, -01.22
Vertex 0.40, -0.15, -01.22
Vertex 1.31, -0.15, -01.22
Vertex 0.40, 3.16, -00.38
Vertex -0.40, 3.16, -00.38
Vertex -0.40, -0.15, -00.38
Vertex 0.40, -0.15, -00.38
Vertex -0.40, 3.16,-00.38
Vertex -1.31, 3.16,-00.38
Vertex -1.31, -0.15, -00.38
Vertex -0.40, -0.15, -00.38
Face2 0,1,2,3
Face 7,6,5,4
Face2 8,9,10,11
[Texture]
Load R15FInt.png
Coordinates 0, 0.00, .125
Coordinates 1, 0.355, .125
Coordinates 2, 0.355, 1
Coordinates 3, 0.00, 1
Coordinates 4, 0.35, .125
Coordinates 5, 0.66, .125
Coordinates 6, 0.66, 1
Coordinates 7, 0.35, 1
Coordinates 8, 0.67, .125
Coordinates 9, 1.00, .125
Coordinates 10, 1.00, 1
Coordinates 11, 0.67, 1
Emissivecolor 255,255,255
Transparent 0, 0, 255
[MeshBuilder]
Vertex 1.26, 3.117, -01.22
Vertex 0.40, 3.117, -01.22
Vertex 0.40, 3.7, -01.22
Vertex 1.26, 3.7, -01.22
Vertex 0.40, 3.117, -00.38
Vertex -0.40, 3.117, -00.38
Vertex -0.40, 3.77, -00.38
Vertex 0.40, 3.77, -00.38
Vertex -0.40, 3.117,-00.38
Vertex -1.31, 3.117,-00.38
Vertex -1.31, 3.77, -00.38
Vertex -0.40, 3.77, -00.38
Face2 0,1,2,3
Face2 4,5,6,7
Face2 8,9,10,11
[Texture]
Load R15IntRound.png
Coordinates 0, 0.00, 0
Coordinates 1, 0.34, 0
Coordinates 2, 0.34, 1
Coordinates 3, 0.00, 1
Coordinates 4, 0.35, .125
Coordinates 5, 0.66, .125
Coordinates 6, 0.66, 1
Coordinates 7, 0.35, 1
Coordinates 8, 0.67, .125
Coordinates 9, 1.00, .125
Coordinates 10, 1.00, 1
Coordinates 11, 0.67, 1
Emissivecolor 255,255,255
Transparent 0, 0, 255
[Meshbuilder]
Vertex 0.40, 3.64, -00.38
Vertex 0.40, 3.64, -01.22
Vertex 0.40, -0.15, -01.22
Vertex 0.40, -0.15, -00.38
Face2 0,1,2,3
[Texture]
Load R15FIntCab.png
Coordinates 0,1,0
Coordinates 1,0,0
Coordinates 2,0,1
Coordinates 3,1,1
Transparent 0,0,255
Emissivecolor 255,255,255
;Rear End Bulkhead
[MeshBuilder]
Vertex 1.31, 3.1, -00.37
Vertex 0.40, 3.1, -00.07
Vertex 0.40, 3.7, -00.07
Vertex 1.31, 3.7, -00.37
Vertex 0.40, 3.1, -00.07
Vertex -0.40, 3.1, -00.07
Vertex -0.40, 3.7, -00.07
Vertex 0.40, 3.7, -00.07
Vertex -0.40, 3.1,-00.07
Vertex -1.31, 3.1,-00.37
Vertex -1.31, 3.7, -00.37
Vertex -0.40, 3.7, -00.07
Face2 0,1,2,3
Face2 4,5,6,7
Face2 8,9,10,11
[Texture]
Load R15_bulk0.png
Coordinates 0, 0.00, .125
Coordinates 1, 0.34, .125
Coordinates 2, 0.34, 1
Coordinates 3, 0.00, 1
Coordinates 4, 0.35, .125
Coordinates 5, 0.66, .125
Coordinates 6, 0.66, 1
Coordinates 7, 0.35, 1
Coordinates 8, 0.67, .125
Coordinates 9, 1.00, .125
Coordinates 10, 1.00, 1
Coordinates 11, 0.67, 1
Transparent 0, 0, 255
;---------------
;Car's right side
;---------------
[MeshBuilder]
Vertex -1.31, 3.10, -00.37
Vertex -1.31, 3.10, -15.32
Vertex -1.31, 1.67, -15.32
Vertex -1.31, 1.67, -00.37
Vertex -1.31, 1.67, -00.37
Vertex -1.31, 1.67, -15.32
Vertex -1.31, 0.80, -15.32
Vertex -1.31, 0.80, -00.37
Vertex -0.80, 0.80, -00.37
Vertex -0.80, 0.80, -15.32
Vertex -0.80, 0.00, -15.32
Vertex -0.80, 0.00, -00.37
Face2 0,1,2,3
Face2 4,5,6,7
Face2 8,9,10,11
[Texture]
Load R15.png
Coordinates 0, 0, 0.150
Coordinates 1, 1, 0.150
Coordinates 2, 1, 0.55
Coordinates 3, 0, 0.55
Coordinates 4, 0, 0.551
Coordinates 5, 1, 0.551
Coordinates 6, 1, 0.78
Coordinates 7, 0, 0.78
Coordinates 8, 0, 0.781
Coordinates 9, 1, 0.781
Coordinates 10, 1, 1.0
Coordinates 11, 0, .98
Transparent 0, 0, 255
;Right Side Interior
[MeshBuilder]
Vertex -0.50, 3.70, -00.07
Vertex -0.50, 3.70, -15.66
Vertex -1.27, 3.10, -15.32
Vertex -1.27, 3.10, -00.37
Vertex -1.27, 3.10, -00.37
Vertex -1.27, 3.10, -15.32
Vertex -1.27, 1.67, -15.32
Vertex -1.27, 1.67, -00.37
Vertex -1.27, 1.67, -00.37
Vertex -1.27, 1.67, -15.32
Vertex -1.27, 0.80, -15.32
Vertex -1.27, 0.80, -00.37
Vertex -0.80, 0.80, -00.37
Vertex -0.80, 0.80, -15.32
Vertex -0.80, 0.00, -15.32
Vertex -0.80, 0.00, -00.37
Face2 0,1,2,3
Face2 4,5,6,7
Face2 8,9,10,11
Face2 12,13,14,15
[Texture]
Load R15SInt.png
Coordinates 0, 0, 0
Coordinates 1, 1, 0
Coordinates 2, 1, 0.150
Coordinates 3, 0, 0.150
Coordinates 4, 0, 0.150
Coordinates 5, 1, 0.150
Coordinates 6, 1, 0.55
Coordinates 7, 0, 0.55
Coordinates 8, 0, 0.551
Coordinates 9, 1, 0.551
Coordinates 10, 1, 0.78
Coordinates 11, 0, 0.78
Coordinates 12, 0, 0.781
Coordinates 13, 1, 0.781
Coordinates 14, 1, 1.0
Coordinates 15, 0, .98
Transparent 0, 0, 255
Emissivecolor 255,255,255