I use two 3" twin mattresses slaying directly on the uninsulated, but with 4 coats polyurethane, 3/4" plywood floor of my trailer. I use rubber-backed floor mats as insulation.

- floor mat.GIF (54.42 KiB) Viewed 2218 times
On two sub-50 degree occasions, the interior walls sweated, but I found no condensation under the flooring mats (cut to cover the entire floor). Since I never have camped in cold weather, I thought further insulation not necessary.
A side note:
my badly-positioned canopy dumped directly onto my not-tightly closed door, all day, during a monsoon-like trip; I returned to a trailer with 1" of standing water on the floor-worse than condensation! I sopped up whatever water I could, sealed the leak, and waited 'til I returned home to dry out. No damage done. However, I often had to sleep in the back of my old '75 Chevy pickup with aluminum topper, then later, in the back of my '09 HHR Panel, when hunting or when trapped at work by ice-storm weather, 60 miles from home (during that season, I often would only have 6-7 hours between shifts-I wasn't going to drive anywhere!). My insulation from the cold seeping up was air-filter media covered by a thin foam camping mat.

- filter media.GIF (41.3 KiB) Viewed 2218 times

- camp pad.GIF (36.55 KiB) Viewed 2218 times
Along with comforters, and a sleeping bag (20 degree rated), and sometimes using a Lasko my-heat, I was comfortable down to 10 degrees. I think these would serve against condensation as well. now retired, I no longer have to sleep in my vehicle, just my trailer, by choice.