I always covered our last TT and that paid off in spades at trade in. It was also nice to have a 13 y/o that looked like new.
RV's are made of junk materials that just don't stand up to the weather. You cant begin to compare them to a house - nothing is the same.
The sun is especially hard on graphics, caulking and roofs.
Our ADCO cover finally wore out and I didn't cover it last winter. I was amazed at the wear it suffered - especially to the roof. The white material coated the gutters with itself and it came out like long rubber bands. It was only the seoncd time I ever had to touch up the caulking too.
The more you can keep them out of the weather, the longer they will look, smell and work like new.
With a acover I would uncover it in the spring and it would be fresh and clean like the day I put it away.
In the end, I got at least 40% more on trade in than I would have (from the historical data I collected).
So it not only kept the rig nice, it paid me back thousands of dollars.