The ViewStar is an excellent controller. You can also just dangle it from something up above using a shoelace (not kidding!) instead of putting it against the wall if that will let it get more air around it.
If really need more venting for that cargo bay, you can also put a "cable hatch" in the door. This can be closed while on the road to keep water and dust out, open while camping, and still lets you close and lock the door.
I have one for passing wires in to my inverters and for the solar controller to panel out on the ground outside wires. Also acts as an air vent. Works great.