The Dry Ice thread tripped my idea switch.
Some float-hunters cool their meat by placing it in plastic bags and submerging it in the river. This works OK as long as the bag's don't leak. All in all this method is risky since trash bags are thin and easily damaged, and wet meat doesn't make for great table fare.
So here's the idea (maybe someone's already done it).
Space Bags. The wife bought some to save on closet space. They're pretty thick (4 mil I think) and come in a variety of sizes. The largest could probably hold a bone-in moose quarter. Rigging up an adapter would let you use your raft pump to vacuum out the air.
Advantages: watertight, durable, and bug proof
Disadvantages: storing raw meat in plastic is a gamble and only works if the meat is kept cold.