Metal fuel tanks can be renewed, but you need to know first how bad it is. Several places make restore kits for tanks, Eastwood is one for example. IMHO, I'd pull the tank, inspect it thoroughly, then decide the next step. If it's really corroded, I'd opt for a replacement poly tank. Another option would be a camera inspection before you tear it out. I bought a camera from China several years ago with 25' cord/USB for sewer inspections and now I seem to use it more for other things. Point is, that camera was like $20-25, video displays on my laptop. I couldn't rent one for that price. I don't know of any resto kits that work in place, you have to be able to move it around to clean and coat the inside.