The biggest challenge will be keeping the barrel from falling apart as it dries out. Well, maybe not the biggest challenge, but a major one I think. The staves will shrink as they dry out and the whole thing will become shaky and eventually collapse like a house of cards. Screwing the hoops to the wood staves helps considerably, but it will still be quite shaky and it will be leaky in every sense of the word. I do like the concept though and if you can figure out a way to stabilize and seal it, it would be a cool project. I'm thinking you might be able to spray the inside with something like fiberglass rosin to create a lining and hold the barrel together. I don't know how you would go about doing that, but I think it would work.