Collision issues

Hey guys, I'm currently working on fixing some collision issues with this tesla model.
The problem is that some parts (bumper front, bumper back, sideskirt) don't seem to have proper collision (clipping into walls).

I've tried different methods in zModeler but with no luck. It's worth to mention that I'm not the most experienced guy when it comes to editing vehicles.
- extend the chassis COL to include the bumper
- change the existing bumper COL to be bigger
- add a completely new box COL for the bumper

It seems like the COL "falls off" after hitting something. If I go slow, it works fine (most of the time).

Anyone experience something similar, or can give me some advice?
Thanks in advance!