Marmots in Mineral King chew cars - plastics and rubbers and chewy bits. You have to take chicken wire or heavy tarp to wrap around your car at the trailhead. Rats and squirrels could probably take on a tupperware, coons can open them. Polycarbonate ala BearVault stops them, so does the heavy duty plastic of the Garcia or similar canisters.

IMO buying a rat sack is cheaper than trying to make one - why reinvent the wheel and spend all your time on what's already available for cheaper (by the time you get done with the prototype how many hours will you have spent that you could have used for something else, like work, hiking, playing with your kids, etc)? Do it only if you need a hobby to take up a bunch of your time.