1. triangles is not a valid section, to add collision triangles you're meant to use submesh. See https://docs.rigsofrods.org/vehicle-creation/fileformat-truck/#submesh. Example:
submesh
cab
;the format is node1, node2, node3, flags (c for collision)
0, 1, 2, c
0, 2, 3, c
...and so on.
2...