Ben, I have not run into any issues with temperature up here in Wisconsin with top coats. I have fished mine in 0 degree weather when the water is right around freezing and hasnt played any adverse effects with cracking or chipping.
I actually have a boat load of different top coats depending on the bait. For more weight sensitive Etex, MCU, or AC1315. Etex for most of my normal baits, and Devcon for toothy critters, although MCU does hold up well due to it having some give (less chipping)