Not sure why Jayco bothers with the tank pads, because as everyone has already stated, you still freeze your piping. To answer your question - the pads are installed on all three tanks. If the temps are hovering around freezing, I won't bother turning them on till we get to camp. I figure all the movement while driving should keep things in the safe zone. Remember, you need to have some fluid in the tanks to use them. If it's really cold, sub-25, I'll turn them on while driving and throw some antifreeze in the black/grey tanks. After awhile, it mixes and keeps the discharge piping from freezing.
Brian, Mary, kids, beagle - Moose, and mutt - Maggie.
2012 Greyhawk 31FS
2013 Ford Explorer Toad