Are you storing it with the mast up?

My advice is to just cover the trampoline with a tarp. The tarp is only for sun protection, not to keep the boat dry. Cut a bunch of holes to let the water run through. If you don’t 100s of lbs of rain water will collect on the tarp. Keeping the sun off your lines and tramp will greatly extend their lives. You can just use an 8’x8’ blue tramp with bungee cords. Put it on after trailering or when you are done sailing.

If you really want to cover the whole boat, you can get a custom cover made out of a fabric like sunbrella. It is costly. my club has boats that have sat in the sun for 25 years and are ok. You can use regular car wax to protect the hulls from the sun, if you like. If you use a tarp just make sure water does not pool on it. It gets really heavy quick.

Good luck.