I would echo Jon's comments about the use of Cruisairs when running down the road. If you want sweat running down your Lewcrack, that is a good way to get it started.

To the rest of the conversation.........

Plenty of Storage Space - Way Good
Plenty of Cooling Capactiy - Outstandingly Good

I don't care if I can stuff an army of pigmys under the coach, if it becomes a sweat filled torture chamber while running down the road, no one will care how much extra stuff resides in the bowels. Living in South Texas, it is highly unlikely that I will own a coach without OTR air and that cooling has to comes from somewhere, so taking X many BTU's, however you get it there, will cost you something.

If someone wants to take the time to figure out all the energy / efficiency / cost numbers for using roof air / cruisair / Webasto / driver air / OTR air, then so be it. It just looks like a math equation to me and I am comfortable with the use of space vs having to have an onboard HVAC person to keep it all sorted out.