The oven does put off some heat but mostly out of the vent at the rear of the stove top. The door seems to be insulated very well so there is very little appreciable heat radiating from the front. I just had the Fantastic fan running and the vent window to the right of the stove opened. Didn't get too warm in the trailer at all.
Custer is a beautiful park. It must get a considerable annual rainfall because everything was absolutely lush green. There are animals all over the place so you do have to drive cautiously. We saw Mule Deer, Bighorn Sheep, wild Burros, wild Turkeys, and, of course, the wild Bison. In my opinion, the BlueBell and Legion Lake areas offer the nicest camping. Legion lake was as calm as glass and deep, deep blue. Its a good sized lake and you can fish or rent paddle boats. I'm not sure how close the park is to the battlefield (Little Bighorn, I think?).
Anyway, would recommend Custer State Park to anyone and suggest that you plan at least one full day to take the widlife loop drive and see some of the sites.