I had just removed a tank from a 93 truck I bought that had been sitting for over two years. The tank as you could imagine the tank was a mess inside. The fuel pumped was staining because the screen was so clogged up.
There was only a few minor rust spots that I ended up treating with this por15 fuel tank sealer.
http://www.por15.com/bSPECIAL-Quart-of-Fuel-Tank-Sealer-Quart-of-Metal-Ready-b?sc=2&category=180I was only going to treat the rust spots but I ended up coating the tank half way up to the seam. I can't testify to the long term durability or effects of the coating on the EFI because I only have 1000 mile on the truck since getting it running.
Por15 sells a degreaser (marine clean) that should be used to remove any gas residue. then you need to treat the inside of the tank with the metal ready to chemicly etch the metal for the tank sealer to bond.
Here is a link I found while I was researching a good fix.
It's a very good step by step process.
http://inetogether.net/jaguar/041101.php
