The only thing about water (and dust!) you can garantee is that given sufficient exposure, it WILL get EVERYWHERE. I spend 6 months of the year with water on the ground, water in the air, and condensation everywhere else. Just slow it down where you can, and make sure you have good drainage! For computers and fuse blocks, silicon seal them into tupperware containers with air/watertight lids, and have some silica gel desicant inside to take care of ambient humidity changes with temp.