We use reflectix, memory foam and electric blanket but for 3 different reasons. 

I installed reflectix in my bunk windows to limit the cold air blowing through the canvas during the winter months.  There was enough that I also installed a layer under my mattress as a barrier for the wind that blows under the bunk end.  I did not install any on the plastic windows in the main area of the camper because the plastic stops the wind and not being able to see out of let light in would definite the purpose of being outdoors.  I could just sit in my basement in a sardine can and get the same effect.

I added a 4" piece of memory foam under the mattress on our side only. (Bought it from overstock.com)  This adds some insulation but is mainly for comfort.  Never being told that I am a small guy, I could feel the wood through the mattress while sleeping and I found myself rolling around at night because I could feel my hip bone.

We carry and electric blanket in the camper which is cheaper than a heated mattress pad.  If it a cold night, we plug it in and warm up the bed before going to sleep.  Feels like putting on a warm pair of jeans that just came out of the dryer. I only keep it on overnight it the temps are very low, like the teens.  The electric blanket is a big hit with my daughter when she's climbing in bed.

All three of these make a big difference in a campering experience, it depends on your goal?