We have an Adco cover for both our horse trailer and Flagstaff 21FBRS. The TT cover is the Designer Series and we are very impressed with the design, quality and price.
Purchased from Camping World on-line, the best price.
The TT cover has vents and full access zip-up on the entry side. Also, the roof material completely covers the roof and overlaps the sides. We have had a few very strong wind storms and held excellent. We added a few ropes around the sides to ensure a snug fit.
Finally, use tennis balls on the rain gutters (X) and foam noodles on the bottom corners to prevent tearing.