Well I am slowly getting done installing my second layer of foam insulation. Last night I had my very first mini test run with the new layer of foam board. It dropped down to freezing 30° and the inside temperature with only the TV and my body heat was 52° this morning. With 2 people the temp would have been 57+ deg F. I am now even more convinced that with approximately 2 inches of foam board insulation R-10 inside the plywood, one would be able to keep warm down to 10 deg without any great effort or heating required. Its not to bad to live with 50+ deg , its not that hard to get used to, at least for me. Currently I only have R4 with 3/4" of blue foam board onside of the plywood. There is a layer of foam between the metal siding & the interior plywood.
The same effect would also work for AC in the summer time as the foam board would keep the heat out & allow quite a large trailer to be cooled to 70 deg with only a 5,000 Btu AC running part time. I would estimate that 2,500 - 3,000 Btu would be adequate for cooling.
As I get a chance I will also try to post some more pictures in the next day or so.
Soon the new trailer is coming , details to follow. Thank You - to all the people at Carmate Trailers.