I think that’s an unfortunate consequence of the game having no concept of shooting from high ground, so the projectiles from turrets will always hit your vehicle if it’s in the way. Dumb, but not an easy thing to fix.
Problem is that boards are on the same location as trunks, seats, etc, so they can’t just have a unique z-level. (And again, most people don’t armor the innards of their cars, as there’s little benefit to it - armor protects from direct damage, and shock damage ignores armor, which is a separate issue entirely.)
The whole problem still comes down to “of the 7 parts in the square, which one do you display if you can pick only one?”, and listing out every individual part in order of preference isn’t really an option - not only would it be difficult to maintain but chances are the next person along is going to disagree with the ordering.
I don’t think you’d need to worry about trunks or seats unless they’re broken, either. The most important parts would be the ones you can directly interact with (welding rig, kitchen unit, forge, etc) and parts that experience Critical Existence Failures (engines, gasoline tanks), both of which are internal and shouldn’t show up on top of other things anyway.
Anyway, the armor-colored parts are probably an easy fix with a menu option. Z-levels would probably need something where you can edit the JSON to specify the Z-level, and if you omit it it assumes a default based on the location (as it does now). “Highest on the vehicle” is then a sane default, while allowing customization by the user.
