Our 2007 is not so bad. On very long drives the dog house gets uncomfortably warm, but not hot, for the passenger from heat soak. We are talking hours of driving with just short gas brakes. In our RV the passenger (either me or more often the wife) will simply move to one of the other seats.
The dash AC will cool the complete RV (27 ft Lazy Daze) if I open the rear most vent hatch a small crack to let the hot air out. I am sure the air flow is also taking any heat soak in the cabin with it.