I only can give you my experience with Clayton 2.5 Overland.
I have true 37" tires and been on some 7-9 trails in California.
I set it up per the instructions and I only have rubbing on the rear inner liner, but all 37' rub there. No bottoming out, but I have a 1.25" spacers on my stock...
JCR Overhead Molle, yes, drilled 2 holes in window frame to mount. I know you were just looking to mount the head unit, but you can mount all kinds of stuff on this thing and clear of the rear view mirror.
Lol, I have the Clayton Overlander 2.5 kit and the rear sits higher than the front. I've been looking for more crap to put in the back to level it out. Their 3.5 Overlander springs might do the trick. Like in the comments above, make sure they work with your shocks.