The easy option is to just buy one of the aftermarket seat pads that you just place on top of the seat and you sit on the pad. They just plug into the cigarette lighter.

Not the prettiest option, but it is the easiest.

 

Would the seat heaters be your only heat? If you don't already have heat coming out of you ducts, there is plenty of room in your heater box for 3000 watts of heat. 3000 watts of heat will blow 160 degrees Fahrenheit out your vents. I can't tolerate mine up like that for long before I need to dial it back to 1500 watts.

 

you really need duct heat to clear the windshield..... so why do you need seat heaters on top of that? 1500 watts is only enough for mild cold, you need 2500-3000 for cold....

 

If the seat covers come off, which I'm pretty sure they do and are not bonded, I recommend using the Rostra brand heaters. I've installed various brands and the Rostras are the best packaged, best performing that I've found. They'll set you back around $100 per seat, but have a good functioning variable control versus high/low settings.