Yes, cab must come off or you can patch it in place. Drain and clean tank interior and clearly ID the leak. Cot leak with POR-15 and allow to completely cure. Apply a 2nd coat of POR-15 and embed the fine mesh fiberglass into the uncured POR-15 and allow to cure. Now overcoat the fiberglass and POR-15 with PorPatch and allow to cure. Coat the entire patch with POR-15. You may want to apply a couple of coats of POR-15 on the exterior and fill any craters with PorPatch. I have a 212 tank that I patched this way over 5 years ago and it is sitting with 25 gallons of fuel in it and no leaks. POR-15 is not cheap but it will beat the cab removal, http://www.por15.com/ A light, air tools and your arm will fit through the fill opening.