One man's memory foam is another man's "memory foam." I don't think all "memory foam" (a marketing term that probably has very little real, "legal" meaning) is the same. Actually, we can be certain that each company's "memory" foam is likely different from another's.
The Walmart memory foam must have a different forumulation than Tempurpedic, for example, bcz Tempurpedic memory foam would be useless or worse in our Teardrops in sub-freezing temps. My Tempurpedic mattress gets harder in 60 degree temps, and I am certain it would be even harder in 50 or 40 degree temps. In our TDs, your body would warm up the foam, eventually, and a good comforter would keep it soft enough through the night, I'd think, but I think it would be pretty hard by the next bedtime (unless the TD were parked in the sun and really stayed warm during the day - how much do our TDs experience heat gain during a cold day? Is it warm in a TD parked in the sun when it is 30 degrees outside?).
I'm not sure which foams are best. I'd probably opt for the least toxic one,...but that might not be the most comfortable, so.....
If anyone does any sleauthing on this, I'd be interested. We haven't pulled the trigger on buying any topper. So far I am sleeping pretty well in my TD, so....
but I have been thinking about it
-Al