http://www.amazon.com/We-Sell-Mats-Interlocking-Flooring/dp/B003R2JATU/ref=sr_1_1?ie=UTF8&qid=1386614689&sr=8-1&keywords=wood+grain+interlocking+foam+matsI'm ordering these after the first of the year and covering my whole floor, inside, where I can clean it and keep bugs/moisture/sand out. They'll help, no doubt. To what extent, I'll let everyone know next spring.
Where I camp, it gets down into the 20's in JUNE, and AUGUST! Gaining 30 degrees above outside with a ton of insulation and way too many hours of labor while using no heat gets me nowhere. Besides, I want my inside "heated" to 75 or so, not 50-something. (sorry OTC, I love your technological analysis and motivation, but many of us aren't camping in the tropical confines of the west coast, and aren't going to be warm without heat even if we had 6 feet of insulation covering 100 percent of the trailer. 20-something degrees is just an average cool spring or fall night in the Rockies, and if its 29 outside, I want it warmer than 60 inside. )
So, I'll keep watching the nice little flame flickering through the glass door of my beloved heater, blowing warmth all around, providing a place to warm the toes and lie comfortably on top of the bed. And I'll be putting some foam on the floor. The plywood walls will have to endure for now, with their meager factory sheeting and cold hard beams. It's already passed the 20-degree test without the floor covering though, so I'll be good to go for just about anything.
Just for fun, I'm considering going out on one of these 0-degree afternoons I'm having lately and firing up the heater for a couple hours just to see how warm it will get inside. Maybe a before and after test with the foam mats. Plenty of 0-degree days and nights ahead in the next 60 days. I'm not that frozen-in yet, but getting there.
