Go for as much ventilation as possible. Also, try to keep the sun off the boat as suggested above. It's a boat, so water
coming down on it won't hurt much.
I would recommend installing a "garboard drain." This is a removable pipe plug
installed in the lowest part of the bilge
so it will drain completely. The idea is that if the boat does get water
inside, it will drain out. In our area marinas
sometimes just drill a 1/2" hole in the bottom of the boat and patch it before launch.
If you have any varnished exterior woodwork, make sure the finish is intact.
As stated above, 3 months isn't really long for a boat to sit.