We once cleaned an apartment block that had boxed in water pipes running up an outside wall to supply all the upstairs flats with water.
It seemed to work to begin with, but I don't know how long it lasted over time as the builders went bankrupt and HMRC seized both apartment blocks.
There was another windie further north who couldn't heat his van due to street parking, and also fitted 12v heat trace to the pipes from his tank to the pump and from the pump to his van port. Seemed to work for him.
I would think that keeping your r/o frost free is your main concern. I know of one cleaner who had his Merlin sitting on top of his IBC tank all wrapped up in bubble wrap. The 'warmth' from the water in the IBC tank stopped the r/o from freezing up. His setup was in a metal shed in his back garden. Granted, we live on the North Coast so don't experience the same temperatures others will do inland.
There are a few windies locally who produce water into IBC tanks in their back garden. During the very bad winter in 2010/11 (was it 2011/2?) which effected the East Coast for approx 6 weeks, the IBC tank in our garage never had ice in it. We drained most of the water from the tank in my son's van, and the little that was left in the bottom froze up solid. We drained the pump and inlet filter of water, so no damage was done to those components.
