get a sham-wow towel. They soak more water and squeeze dry. Make your pup sleep outside for a month or two before hunting season. Start a good conditioning program if your dog isn't active outside of hunting season. 6 weeks before hunting season get on a balanced food. High protein foods do not help dogs put on body fat which is needed for sustained hunting. Get a lower protein higher fat food started 6 weeks in advance.
Everything takes around two months to make a difference. From acclimation, food change, weight gain and conditioning.
Worst case, take a kennel with a cover, put the dog away to warm up when he starts to get cold. Make sure there is a mat in the kennel to keep the dog from sitting in a puddle of water. Do your best to always run them to get blood circulating and dry them before kenneling.