I've messed around with a lot of classic motorcycles over the years and have seen some coatings fail that were done by professionals. I will never use one again personally. Next time I run in to an issue I plan to try this stuff
https://www.workshophero.com/products/metal-rescue/
If you're not interested in something like that, my advice would be to get as much of the loose crud out of there as possible and be diligent on replacing fuel filters. Avoid ethanol gas if possible and if not possible, never let the truck sit for extended periods of time without a full tank.
Or bite the bullet and replace the tank.