Bronko have you ever tried them (body Warmers) made by HotHands that have the sticky side on them, you peel off the sticky side and I put them on the outside of the last shirt I wear near my back, usually near my kidneys. These things work awsome. I use two to four of them when it's brutal cold out, they keep you toasty warm and they will last all day from 6 in the Morning untill dark. Just make sure you take em out befor your drive home as many a time I had to stop the Truck and get them off as my back was on fire!
They sell them at Wal-Mart or wherever else for $2 a pack, you get 2 of the body warmers and 2 small hand warmers with them. I also buy the Big Body Warmers without the sticky side on them and put one in my mitten and the other in my pocket. With all of these Im good to go even when it's Zero out and -20below windchills.
Happy Hunting and stay Warm!
(BP)