The downside issues I have heard and spoken to people about that are not listed:
Weight - 5/8" panels are heavy.
Wall & Ceiling joints loosening up over time & miles.
Cabinets not having enough support on walls.
You are going to find +/- with either type of construction, it all comes down to how well the materials are used to get more +'s.
As for insulation, you can insulate the box area like a refrigerator, but if you do not do the same to the cab then you are going to loose all of your effiecency. You cannot imagine how much heat or cold is lost through the cab, it's huge. If I shut the leight weight curtain I have now it makes a world of difference, but it is not like the R rating your going to get from heavily insulated walls. Some of you guys that are talking major insulation, may want to look at ways to block off the cab with either a insulated curtain or some sort sliding wall.
BTW I have the standard insulation and have yet to encounter a problem with heating or cooling.
2003 28' Show Hauler Motorhome on a 1995 FL 120
www.showhauler.com
[This message was edited by warpath on August 26, 2003 at 04:15 PM.]