It really does depend on where you live and where you store it. I've been using a cover for over 15 years and never had one rip or damage the camper.
I clean my camper exterior and awning before I cover it and if I get 4 years out of a $300 cover it's worth the $75/year to have a perfectly clean camper in the spring...along with any UV protection the cover may have provided.
And yes, the garbage can is a good idea.
Between leaves and pine needles my camper gets quite dirty if it's not covered. I left my previous camper uncovered one winter because of an early snow and I spent a good day cleaning the exterior in the spring...worth the bucks IMO.
