Charlie,
If you put a queen-size mattress in your camper, that’s quite a bit of floor insulation, when you think about it — much thicker than the foam headliner. You get condensation when your warm, moist breath contacts the cool walls. Hence the insulating headliner. With a wall-to-wall mattress, that moist air never will reach the floor. Now, if for some reason, you decide on a smaller mattress, there will be some cold floor space that could get a bit slippery. Don’t do that. The CLC teardrop was designed around a queen-size mattress. We put a 4″ memory foam mattress in our camper and took it out for its maiden voyage last weekend. The temperature dipped into the low 40s in Highlands, NC. There was condensation on the walls in the mornings because we hadn’t gotten all of the headliner installed (just couldn’t wait to try it out) but the floor was fine. We did put a waterproof mattress cover on the mattress just in case some rain gets in as we’re climbing in and out.