I park mine under a metal carport 310-320 days a year. I wash and wax it once a year. We keep the inside clean as well. Kids know not to jump around on the slide or bunks. It is currently in its 8th year and looks pretty much brand new.
Alternatively I've got friends that have a newer camper that lives outdoors 365 days a year and looks beaten down and I doubt it will last as long as mine and it likely won't hold its value as well as I hope mine will.
We'll own this one for about another 3.5 years, at which point I'll retire and buy a 5th wheel for a long cross country trip. That new 5th wheel will also be kept under a metal carport more often than not, so I hope it'll last just as long and look just as nice.
I think the 10 year rule essentially exists to give campgrounds the leeway to turn away junkers that might fall apart in their campground or simply get abandoned in their campground. We camped in several places that had a 10 year rule in our older camper, but the camper was in good shape and we never once had an issue.
