I have a therm-o-rest...not the USMC one though. They're nice. They're light, self inflating, and roll up real tight so you can fit them in your pack and don't have all kinds of shit hanging off. I'd definately suggest a layer underneath.I got kicked down a USMC Thermarest a while back and haven't had chance to try it out yet. How are they? Are they good on wet ground or will they need a layer underneath it (Tarp/Cardboard) to keep it dry?