Temperature fluctuation combined with humidity is your worst enemy. It's fine when the equipment is warmer than its surroundings but bad the other way around. I would store gear in plastic bags with plenty of silica gel... recharge them often. Keep everything in a styrofoam ice chest to slow down temperature transfer. Put the chest in a cool dry place out of sunlight. Try to notice what part of the room stays the most stable in temperature and keep it there... if it's also dry.

Or... you could ask photographers and gun collectors there what they do.