I have a Backpacker magazine from February 2007 that had a great article about sleeping warmer. We've used these tips many times while tent camping in the mountains and I'm sure they can be used with a PUP as well. * Size Your Sack: Get a snug fitting sleeping bag with just enough room for tossing-and-turning space. A too-big bag means extra space to heat. --With our girls, we fold the bottom part of the sleeping bag up on top of them, creating less extra space. We also stuff a blanket around them for extra snug-ness. *Have A Snack: Eat energy bars before bed to give your body the fuel to stay warm, and keep a Snickers handy in case you wake up chilled before dawn. --We encourage s'more eatting and hot cocoa drinking for everyone before bed. Might not be the same type of "fuel" as an energy bar, but we enjoy it! *Cover Your Dome: Always sleep in a hat. --This is a hard one to get the kids to do. *Snuggle With A Bottle: Fill a Lexan bottle or two with hot water, stuff them inside a sock, and place them between your thighs (to warm the blood in your femoral artery) and at your feet. --We do this and the water actually stays warm for quite a while, which is good because no one wants to snuggles with a cold water bottle in the cold! *Dress For Space: Putting on too much clothing can make your bag tight and compress the insulation. Adjust your layers to suit your bag's interior volume. --We just make sure the kiddos have their warmest jammies on and we do too. I also wear big wool socks because my feet are always cold. I'm sure Gizmo's and and the reflectix stuff would also be recommended for PUPs, as well as lots of propane! Enjoy the cold weather!