Go to YouTube and do a search for "Heartland Toy Hauler plant tour" and you will see in the video that the roof on the cyclone is closer to 6-7 inches thick. This video was produced August 17, 2015.
Don't trust what the dealer tells you. Do your own research and you will be much the wiser. He wants to make a sale and probably has never even used an RV.
I don't wish to discourage you from purchasing your RV but you need to know the facts not the claims. I have several friends in our RV Club with Big Horns and when it reaches 100 plus the average inside temp is around 78 to 80. The AC units are only capable of changing the air an average of 20 degrees in difference. At zero degrees your pipes will freeze if you don't take precautionary measures such as adding additional heating in the underbelly and that's those equipped with the arctic pkg.
Take a few moments and go to the Heartland site and talk to those who know. They are mostly happy with their rigs but know how they perform in reality.
Walter and Janie Rogers
2012 Sundance 277RL
TV 2006 Silverado 2500 6.0