Grinding outside rust and repainting the outside was done first. I didn't have leaks, so i wasn't worried too much about having to repair the tank in that sense.
Esteban, i used a KBS coating fuel tank sealer kit. #53000. about $70. The key seemed to be in the prep work. inside had lots of rust and rust flakes. Took it off and filled it with a lot of media (bolts, nuts, washers) and rolled it around for what was probably an hour to loosen the crud and get the lions share loose. After that, many rinses with water and then the KBS rinsing and bonding/etching agents.... then the final coat....final coat had to be poured in, all holes plugged and then rolled around for a couple hours as well, then extra poured out.. Took a few days of waiting for things to dry in between steps....
finished it off with a new fuel sending unit from ebayer anpira83 from colombia. Works perfect, much more accurate than the old crusty one that was in there.