I've found that covering my boats not only keeps the hulls and trampoline in top condition, but also REALLY increases the resale price.

I originally used a tarp but got tired of it blowing all over the place, water pooling, etc. It also looks messy and isn't a good solution for mast-up storage.

I ended up having a custom cover made by a sailmaker that fits the boat like a glove. The cover works for trailering and mast up or down storage. The custom cover fits around my trapeze lines, spinnaker pole bridles and it even covers the hulls underneath the trampoline.