I warm my packs to right around 100 deg F (38 deg C) for best performance. On warmer days I just leave them on the tailgate of my truck. I also will put them on the dashboard (solar oven) or on the floor of the truck and run the heater. I also have an electric heating pad that I use when it really is too cold or cloudy for those other things.

Warming packs is no big deal to do.