Lee, most of us use something like the pic of I have of mine below. It's a Maradyne 5000 box and it's about as simple as it gets. Little doorways on the sides that open and close and there's a fan built in as well with ducts that can go up to the dash defrosters. Mounting bracket and two holes through the firewall and you're done. Here are the specs for it:
Model 5000 Heater
