I agree the carport / garage is best.
I believe you get what you pay for. When I had a seasonal site, I tried a cover from CW (I think it was an ADCO) . At the time, CW was selling lower cost covers to attract buyers, I don't know what they offer today.
I have used covers on 2 of my 11 trailers. I found it to be more of a PIA for 2 agile people to install and remove. Every season, I washed , waxed and checked all my caulking a few times each season. IMO, the cover did not lessen that end of maintenance.
What I found when using mine. The roof weight when wet held the cover in place , the side panels would "wave" in the wind , even though tied down.
It caused stress on the 4 corners (from wind) and the cover ripped thru on the corners in 2 seasons (which is about an average lifetime for most inexpensive covers).
I never experienced any mold, but some people have.
Since I have used a cover, I see that some people like Calmark covers for longevity and warranty. Only a few had issues with them and I think, it was due to the installation of it.
I found info on those covers that explains the stress , which I experienced.
I have no affiliation with this cover company, im offering the link for info only, I have no idea if its a better cover or not. If you decide to buy one, shop around for a price. I know they cost more, but it might be worth it to buy one instead of 2 or 3 less expensive covers.
Calmark rv covers