Why not just put a coat of POR15 on the inside of it? I'm doing a Pepsi Progress right now and it was rough on the inside, I coated it all with POR15, covering the larger holes with fiberglass sheets embedded in the POR and it came out great.
I might do that. I really need to strip the outside first though just to see exactly how bad it looks. I might put POR15 inside anyway to prevent it from rusting again.