Greg, that thermal sleeping bag may be an over kill but I usually get a drawn hunt, (and again this year) in the Breaks in eastern montana and the days can reach 112f and then at night I've frozen my arse off. About 5 years ago I almost stepped on a prarie rattler out sunning itself in the late morning and since, I been using my cabelas sub zero thermal boots that are snakeproof also. They might be a little warm for bow season but it gives me added confidence since these rattlers get no bigger than about 3 ft. I hunt eastern montana totally different than here in western montana. In eastern montana I hunt the coulee bottoms and here I hunt the mountain terrain and and both conditions I've past up shots for being to deep in and the terrain being too difficult in getting the game back in time with such extreme temperatures and also just being too much work to deal with solo.
Good luck and keep us posted.

Bobby