Yes, performance is one thing, putting parts together is another. The collision box (with triangles and cubes as pictured) is as simple as possible, but I do believe the short ends should be flat, not concave. It will be much easier to use these parts that way: imagine z booster attached to that edge (I like it that way) - it will probably by only attached to one of those collider edges, so if it moves, it will not be in-line with the vehicle, hence inducing a rotary movement on the whole. I could draw a picture, but I'm too lazy right now (just came back from work), maybe in an hour or so, if it's unclear?