I finally made it back to the PE dealer today and put down my deposit on the Super. When she was setting up the install appt. she asked the question, do you want single wall or double wall?? I admit, this was something I had not even thought about, I just figured the installation folks would cover that detail. My rough measurements I took indicated to me I have all the clearance necessary to run single wall, besides the clearance, is there any reason I should consider the double over single? I obviously like the price of the single a lot more!