The SMB does have insulation. I don't know exactly what Sportsmobile West may have used or what the R value was. I'm assuming it was just whatever their standard was in 2006. I am a second owner and didn't have it built out. I haven't added any insulation for warmth or sound deadening though.
My SMB is a diesel. The Espar d4 heater is tapped directly into my 46 gallon diesel fuel tank. I can tell you that I love the Espar d4. It's got plenty of BTUs to keep me warm. When at camp, I turn it up to high when it's first turned on and then turn the dial down to about half way. At night I lower it even more. If it is really cold, I lower the top to sleep just to help the heater so it doesn't have to heat as much space. I can reach up from bed and turn it up in the morning about 10 minutes before I get up and the van is plenty warm. If my wife is with me then the heater is set higher most of the time.
I'm not sure how cold it got early in the morning at camp. It wasn't -24 though. That was out in the Lamar Valley where it was colder. I'm assuming it was between -10 and -15. But that's still cold!