I think some of it depends on where you live.
Wind flapping a cover, bad, rubs through paint even.
Wide swings in temp and humidity, bad, condensation and mildew.
Hot sun on the van all day, cover is good.
Lots of rain, hail, acorns, cover is good.
If a carport is legal, and you have room, it may be a better overall solution, though, and it would be a lot easier to take on and off