We purchased a new TT for use at our seasonal site at the beginning of the season. It will sit for almost 8 months unused, so we decided to get a cover. We purchased a Camco UltraGuard cover. Camco does not make a cover for a 40+ foot TT. Since ours is a Bungalow with 8' ceilings, we decided to go with the 40' - 42' cover for Class A motorhomes. We just put it on yesterday. Sadly, Camco did not include instructions with it, but I found instructions online for it. Even though it was for a Class A, it fit well.
This was the first time we ever covered a RV. Our main concern is sitting snow. Our camper is 800 miles from our home, so we can't get the snow off the roof. It took us about 90 minutes to cover it. I really didn't know what to expect with such a long cover, but it went pretty well. All four of us (wife, 16 yo daughter, 14 yo son and myself) worked together and made pretty quick work of it.
The cover is very well built. It has vents at the top that should allow moisture to escape. The fabric looks similar to clothing designed to wick moisture away. Unlike a tarp, if the fabric was to tear, I don't think it would cause any problems with the camper's finish flapping against it. It's very soft. Since it was such a large cover it was expensive at $331 from Amazon. Our only other option was to have one custom map at over $1,000.
-Michael