12V panels = more flexibility of layout, though more holes and mounting brackets and higher cost of panels. Worth considering on a small roof like truck camper. Either PWM or MPPT can be used then, depends on the system and user's priorities.
On a bigger rig, say 23ft trailer or longer, it's easier to use big 24V panels and stay clear of A/C and/or lift panels few more inches to clear small structures.
Old thread with roof rack that I mentioned earlier... Yep, about 5" to the frame bottom. This is a distant past of solar panels, they were expensive and people didn't install more than 200-300W. My point was - you lift panels to clear roof structures other than A/C. From A/C you should stay clear.