I pulled everything out of the truck and put down insulation from EZ cool (floor, bed sides, everything). It helps and for a plus it hushed the exhaust noise in the cab too.
When I had my Samurai the factory heater was pathetic at best, so i replaced it with a mojave heater. They make them mainly for Jeeps. An aftermarket model is not easy on the eyes, but you can nearly cook on them. You can check summit racing or mohave heaters if they are still around.