It was always the on & off thing that daunted me from trying a cover - it's not a chore I would want to do more than about once or twice a year. If that!
I'm surprised to hear the Tyvek cover described as heavy - Tyvek is pretty light stuff. But then, we are talking about a lot of material for a 35-40 RV. Something on the order of 1500-2000 sq ft!
Some other concerns about using a cover that I have heard: (1) you can't run the furnace or water heater to keep things from freezing (a problem in climates where it only freezes a couple times a winter), (2) you can't use the roof vents to reduce humidity (damp climates), (3) it's very dark inside!, (4) if you don't get a custom fit, the door opening in the cover probably won't line up with the entry door (5) small antennas (radio, cell phone, GPS, satellite radio, etc) can poke holes in it (6) you have to store it somewhere when not on the RV - it is big and bulky once out of the original shipping carton