I sandblast and lead line generally. Your method is very popular,although the tank liner is not an option that many use but its very effective. I used it on rare tanks especially motorcycle tanks years back with great results.
Alluminium/diflouric acid or the POR15 equivalent, (cant remember the name)works ok and is sublte but it needs to coat the whole tank all at once to make it an easier quicker job ...
But your method is pretty much how many do theirs and is quite effective in most cases.
If the tanks are too bad,just get another one,there are quite a few around and they dont cost much....less than the time it takes to clean in some cases
