GSP's have a lot of drive and that constant movement does tend to keep them warm. They don't do as well if they are not able to move much or are wet. A really rainy day with a hard wind in the 30's may also require a neoprene vest. Because they have so much drive your dog can get frostbite if hunting in snow in really cold weather without showing much outward symptoms. They're pretty tough but not invunerable. Lewis dog boots makes a rubber boot with no vent holes specifically for snow and ice. I don't think you should hunt the dog in snow, in temperatures under 20 degrees, for more than about an hour at a time. My dog lives indoors though and an outdoor dog is likely less sensitive.