I would think that there is some risk in affixing something like that to a CO2 tank. If it says "do not allow direct contact with skin" it is definitely not a good idea.
Maybe I am being paranoid, but nitrogen is probably a better idea.
Insulating your hopper won't do the trick.
The reason paint gets cold and brittle, is because on most sides it'll be in the box, outside, or semi-outside, placed on the ground. If possible, keep it stored in a heated car.
Get one of those large insulated bags, and put your paint and heated pads in there. Aldi, a local cheap store do a ski boot bag which would be ideal, for £5. Also doubles for a small kit bag.