Aftermarket has lots of options for heat. Diesel (espar) or propane (suburban) are popular options. You can find knock off versions of each if those are too expensive.
Just back from a 5 day road trip.. First touch of summer temps for me up in Canada. No plans to remove the rear heater/AC unit. Was really nice to fire up the dual AC (cab and box) when back from climbing and chill everything down on the way back to camp.
