We had a tyvek cover here in the northwest and water still soaked through and got staining that we had to clean. My in-laws had a 5th wheel parked outside for 8 years, it developed several leaks and was pretty much for scrap value as a result when it was sold later for less than 10% of what they paid for new 8 years earlier.
With our 2001 class C we recently purchased, I swallowed what I see as a cost of ownership and started renting covered storage. Keeps it out of the rain during much of the year where ducks could drown in the streets and keeps it in the shade in the summer.
The immediate benefit is that it stays pretty clean, I can start and inspect it regularly and we can take it on trips at short notice. No worries of leaks.
History: '08 View, '05 Chinook, '01 Jamboree 24D, '78 Apache Popup, 81 Komfort Tlr,
84 Mazda B2000 'w canopy,
Tent from wedding shower in '96