The parts suppliers,(L.M.C.,Jim Carter,just to name a couple,:see "Links") offer a battery "drop-down" box. I'm not sure how difficult it would be to access,with battery under the floor. Seems that it is designed for that application,though. I don't recall seeing too many pick-ups with battery boxes bolted to the outside frame rails,(behind the cab),as is quite common on bigger trucks.They have more space for fuel tanks,tool/battery boxes,etc. Hope this helps.
