If he's open to hedging his bets, you might be able to persuade him to put a significant fraction of the money into one or more banks. Use the argument that if there's a fire or robbery, he'd only risk the money on hand, and if whatever he's afraid of regarding banks happens, he'd only lose the bit in one bank at a time.

Obviously an imperfect solution, but it'd be an improvement over what he's doing now.

As for the fireproof safe or bag, do some research to find out what parts of a house tend to be safest from fire. It's usually going to be in the basement or on a slab, and away kitchens, fireplaces, and garages where fires often start. It's possible that a fireproof safe heats up so much that paper inside it ignites even when the safe itself remains intact.