[Jeeper6]

I only cover mine when I leave it parked outside for a couple of days due mainly to bird crap and the trees shedding other stuff all over it.
I do worry about the sun and rain effects, but when you think about it on a trip away towing the van it is left outside in the elements, in the case of our lap this year, for 6 months...rain hail or shine.

I use a windscreen shade when left in the sun at a Park, otherwise it is uncovered. If I was leaving the Jeep anywhere for an extended period I'd use the sun screen over the windscreen, and maybe a couple of sheets or towels over the seats to protect them from UV. Though most of us have window tint that cuts back UV.
The car will breathe anyway through the internal venting...