Shortly after I bought the 1998 F150, I ran an 8 gauge hot wire with fuse from the battery to beneath the rear jump seat in order to provide axillary power. Bought a 400 watt inverter, controlled by its switch, mounted it on a piece of plywood and soldered it onto that wire. Works like a champ at a flip of the switch. I have run a 3/8" drill with no problem much less charging laptops and camera batteries. Only downside is I recommend running the truck engine after 30 minutes or while running high load accessories.
Al