Well you could trade in the truck for a delux model, or stop by a local junkyard and FIND a truck with heated seats, bucket seats for that matter (provides much better support than bench seating) perhaps find a Cadillac Suburban with heated and cooled seats that are leather? They should be a direct bolt in fit for your factory seats.
You could also check with a local upholstery shop, or body shop and see if they have any suggestions. I was watching "How it's Made' and they did car seats tonight. IT showed how a heat pad is installed on this model, and the wires run down under the seat for hookup inside the car. It all looked pretty simple to install.
You could install a couple of three way switches with center off, and have it wired to a relay powered only when the engine is on, with #14 wire going to the area under the seats, so that the shop would be able to connect everything pretty quickly after you arrived. Then you would have the ability to have high or low heat setting for drivers and passenger sides.
In the meantime, try a 500 watt inverter that plugs into a cigarette lighter, and a regular heating pad. The small inverters are only $40 at Costco now. Check the heat rating of the heating pad before trying it out. Remember that a 5 amp heating pad will draw 50 amps from the 12 volt system, so look for something in the 2 amp range, and if it draws that much, you will need to hook up a 30 amp circuit for the inverter, and fuse it right.
Good luck,
Fred.
