Some thing that works great for me are thermal care heat wraps, they are cheap ,odorless & really work well. Those late season all day sits can be tough,but these wraps limit how much heavy clothing you need and make shooting a breeze.
Heres what others say.
Just as the manufacturer says, ThermaCare HeatWraps are activated when you open their hermetically sealed package. It takes about 1/2 hour for the wrap to fully warm up. The wrap is lightweight, odorless and can be worn very discreetly. Once the wrap is out of the package, just remove the adhesive, and place the adhesive side on your skin, in the area of your back you wish to relax. I suggest you pull the wrap fairly tight while placing it on your back. This will minimize any gaping between your skin and the wrap during
ADL. Of course, getting the wrap afixed to the exact place(s) of tension on your back is key to getting good results!