I intend to cover the underside of my newly installed galvanized floorboards w/ Herculiner. The rest of the undercarriage will be coated w/ KBS rust seal then the herculiner. Should I use the rust seal over the floorboards as well? I intend to sandblast the rest of the undercarriage. Should I do the same to "etch" the galvanized steel? Or, how would I get the best results?