Water condensation from the roof and a electric blanket . I wouldn't take that risk .
My advice and it's been good over the last 3 years is
Extension lead £20
Oil filled radiator £90
Sounds dear , but it's similiar to a price of a Shurflo pump £80 ,RO at £220 , and other numerous parts to break due to ice .
So £90 oil filled radiator - big one - over last 3 years has cost me £30 a winter .
Running costs - I never noticed it .
^^^^ agree.
I also have a large double bed duvet over the tank. As my pumps are mounted on the side of the tank about half way up, the duvet also covers them. If I had an r/o in the van as most are mounted, then the duvet would cover that as well.
I maintain that the water in the tank, even direct from the tap, will help to keep the r/o and any equipment from damage. The duvet helps to insulate the 'warmth' from escaping too quickly.
I have a very old 800 watt convection heater with a frostat fitted. It sits across the back of my Citroen Relay van and have never had a problem with anything frozen in the past 6 - 7 years. (This is my second Citroen Relay.)
However, I'm also the first to add that we don't experience the extremes of temperatures on the North East coast that some do. The coldest winter I ever experienced up until a few years ago was in Reading in Berkshire in 1999.
I believe that the old Omnipole system (they use their own tank design with a large lid) actually had their r/o's suspended inside the tank and submerged in the water unless the tank was pretty empty. I'm not sure whether they still use this system today though.