I thought about those but dismissed them as they only heat the water in the tank. I believe a much better option are small oiled filled radiators set on low. They heat everything including hoses, reels, pumps, di vessels, brushes and of course water tank's. Condensation can be a problem so cover any electrical contacts with a polly bag or whatever and all is well in the morning. Of course, if the air temperature is below -3 or 4 when you start to work, then you are wasting your time as the water will freeze on the glass almost as soon as it hits, regardless of how warm it is when it leaves the tank.