The mesh, say a bodypanel do need thickness, but the nodes/beams don't, they will connect to the nearest vertex. Take a look at the existing vehicles.
A mesh is made of triangles. A single face like this can be usually seen only from 1 side (depending on your normal) But you can also turn on Double Sided option (You can find it in the material editor in BeamNG) Tough, this will give both faces that same lighting. If the face receiving light is illuminated, also the backface gets, resulting in something not right) In this case you better make your meshSolid like this An easy way to do that is using a solidify modifer along with a edge split modifier incase you have some smooth mesh Example: I applied the solidify modifier only to this bumper. While the other parts gets invisible when seen from the other side because I modelled only the "outer" side, the bumper can be seen from all ways without any problems. http://wiki.blender.org/index.php/Doc:2.6/Manual/Modifiers/Generate/Solidify I hope you were asking for that.
