What is the consensus on these gas tank repair kits where you clean, etch, and pour in a liner compound?

I have a small leak near the tank drain plug. It looks like it has been brazed before (or it’s the factory brazing when the drain valve was installed). I have not taken the tank out yet, or opened the sending unit hole, so I do not know how bad it is inside. The outside looks in very good condition with the tar still intact. I think it sat around empty for a long time since the tar only came off at the very bottom as a result of me putting fuel in the tank.

I was also thinking of brazing it myself after washing it out.
What should be used to clean off the buildup on the inside of the tank? I was thinking of cleaning the inside of the tank, filling it with water and then brazing the damaged area. Any suggestions?

Also, after dealing with the leak and interior, I also heard of using some epoxy resin to cover the outside of the tank. Wonder about epoxy resin vs. using rubberized under coating from spray can (chip guard).