Hi,
If the cover is made from nylon ( and a few other polymers) it will change size according to how wet it is. Our Laser 5000 has an undercover that we have to dampen to get it on the boat, when it dries the boat is almost shrink wrapped.
You can see the same effect with tents, they go saggy in the rain and need the guys tightening, when they dry they go taut again.
Canvas behaves in precisely the opposite way, it gets taut when wet.
Mark
