My boat stays on a covered lift with the cover on it during the summer but the weather still gets to it as do the spiders and bugs....
Just as a thought, (I don't know where you live so it might not be an option) try shopping "boat storage" on Craigslist. My buddy has done this with great success. Lots of farmers around here that have barns on property that are no longer in use so to speak so they rent out the space. Most don't mind if you take the boat in and out as long as you work that out in the agreement.