Since peaking, now I'm having issues getting the heat pack to actually heat the box properly when it's put outside. It will hold it at about 10 degrees above room temperature indoors, but outdoors, it sinks into the 50s in the box, in 30 degree weather.

I'm thinking that the solution to this may be to activate the heat packs and let them peak before packing the boxes, then put in 2 heat packs to each one.