Well, if there is a rust issue, we sell this to fleets for their saddle tanks all the time.

I once had to repair a small rust hole in steel gas tank. Here’s how I did it.:
empty the tank completely, remove, flush out with soapy water. Make sure tank does not smell like gas, because if there’s any fumes still inside then you could have a small explosion. Sand area around pinhole until shiny metal. Use plumber flux and tin the area with propane torch and plumbing solder. You should be able to close the hole with solder, use just enough heat toward the end to keep solder from being runny thin. If it wont close up, tin a penny and solder it over the hole. Test result with water in the tank. Blow tank dry before replacing. You may want to use Dry Gas (really an alcohol) to make sure there’s no water left.