I was one of the first people to use Peterson Smoker Pucks, and I almost always use a cardboard box when I smoke in cold or windy conditions. The great thing about the Pucks is that they generate a lot of smoke early, and then produce a lot of heat later. Anything to help keep the heat inside the smoker will greatly reduce your cooking time. I know that many smoker manufacturers don't recommend covering the smokers, but I have never had any problems with the box getting too hot. It is a good idea to keep your smoker away from your house or shop though, just in case the box ignites. Good luck with your Peterson Pucks. In my opinion they are the best product out there for smoking fish and game.
P.S. They work great in BBQ's too. Try a large piece (12-14" long) of elk backstrap seasoned, and rotisserie cooked with 3 or 4 Peterson Pucks on the grill. After the pucks are used up, keep cooking the meat until it is done, slice into steaks, and enjoy!