I first put a heavy plastic tarp on that covers the roof and about 20" down the sides, then I install the 9 y/o ADCO cover.
In the spring my TT still looks like new on the outside and smells like new on the inside.
At a CG this year some other campers and I were inspecting someones new TT when another camper commented that mine must be pretty new as well. They were all shocked when I explained that it was nearly ten y/o.
I truly do not think breath-ability is much of an issue where you live. The most important thing is to keep it dry and out of the elements.
OTOH, if you get a lot of wind then a cover may be damaged.