all you have to do for a tank is make a box of plywood and lay some 6 mil poly sheet in it
I use Zero Rust, have done filler on top in a couple places, but it's just as well to do the filler on bare clean metal, and if you have whole pieces to clean metal the best bet for the long haul is to use epoxy primer .... for under fenders I like a good layer of rubberized roof tar, cheap and does the job
Bill
