Big old tarp for me, usually bought from the local hardware store. I am on, I think, my 3rd tarp since getting the camper. As previously posted (goes for all types of covers) watch the corners, secure it without making it too tight, use ALL grommets and securing points, and it will last years.
BUT - they don't last forever. And YES - I am jealous of those with RV "carports"... lol!
I try to wait as long as possible before putting on the tarp, colder the weather the less amount of condensation / mold under the tarp. I've not had an issue with condensation or mold on my camper (yet, at least).
Covers designed specifically for RVs are better and nicer - especially the ones with a "door" built in so it is easy to access the camper. Being cheap or whatever, tarps have worked for me.