I think another tank might be better peace of mind. I've never used one of the tank liner kits, but they aren't cheap. I've heard they are used a lot in the motorcycle world - kreem tank liner seems to be used a lot. However, if you do a search for kreem tank liners on some of the bike forums, most of the questions are about ho to remove the old kreem that's clumping and peeling off!
POR do make fantastic products, but I've never used their tank liner.
The only new tanks I know of are from minisport:
http://minisport.com.au/fuel-tanks-fittings Not cheap though. If you put an ad in the wanted section I'm sure somebody must have a spare tank in good condition.