My reverse flow pit is fully insulated all the way around and ends. It started life as a 300 gallon fuel tank, 14 ga thickness. We insulated it with 1" of ceramic fiber insulation and skinned it with 20 ga. The firebox is insulated on the sides and firebrick is on the bottom of the firebox. Only the front and top of the firebox are not insulated. It is 5ft long x 3 ft diameter. Takes about 1 hour to come up to temp (250), but that is bringing it up REAL slowly. Once it is hot, it stays hot. I learned that bringing it up to temp too quickly and overshooting - say 300 deg, it doesn't want to come back down. It'll cook in the rain, snow, wind - doesn't matter. Extremely fuel efficient. If you have any questions, let me know. And I use mine in comps too.