I just finished building an insulated box out of rigid styrofoam to house my ro/di unit that is in the garage. Also insulated my mixing tube. Every time I make water I have to unhook the hose and drain it so it will not freeze. Never know when you need to make water in a hurry. It would be a bummer if the hose had to thaw out.
I also reduce the light cycle on the tank by about 1 1/2 hour per day.