If you have a dive shop near you, they have plastic boxes in many sizes by Pelican that are used by divers to store stuff and keep it dry. Here is the sales pitch from Cases by Pelican :
Pelican Case ® built to protect in the most severe conditions:
Lightweight space-age resin: ultra high impact structural copolymer polypropylene, provides 4 times the strength to weight ratio over conventional injection molding, unaffected by dents, scratches or corrosion. Pelican Case meet MIL-STD 4150-J stacking (400 lbs.) Drop Test (48"), Immersion (2" at 160°F). They meet and far exceed the highest standards of industrial, airline, military and commercial applications.
Multiple massive ABS Latches and .250 neoprene closed cell "O Ring" , provides up to 30 feet watertight and air tightness for the ultimate protection.
They have all sorts of shapes, sizes, colors, and some even have clear lids.
ProvWoman