In my experience and sun aint really a problem here in bonny scotland ! is that UV "eats" trampoline stitching ,which left uncovered will start disintegrating apart in a couple of seasons the trampoline material degrades too , but will last about twice as long .

I have no hull covers but I do cover the tramp.

friend of mine had ideal overall cover made of goretex - breathed and was superb.

Breathing covers are essential on epoxy boats too as holding moisture against gel coats can cause osmosis and bubbling when it hits the impermeable epoxy , as for a polyseter boat I guess the moisture heads on into the substrate .

My hulls are epoxy and I hope that anymoisture that gets into gel coat will burn back out on the occaisonal day when the sun does pop out , or dried out by the wind .