I second glen71's thoughts.
I would hate to see all of your blood sweat and tears end up a little on the damp side. It might be pretty difficult to keep a school box dry, they arent' really designed for that i don't think.
Spend an extra five or ten bucks and get a Pelican, Cigar caddy, elec. junction box, ammo can or something that you know is designed to keep out moisture. That will be one less headache you will have to worry about. There are always pelican 1120's and 1150's on ebay.