you keep the inside of the van above zero with a oil filled rad so nothing is frozen, then in the morning when your about to set off turn the water and heater on and let it run for a few minutes so hot water flows through all your hoses and pole,
no messing about with frozen pipes hoses etc and you can go and earn money, the heat from the heater actually keeps the inside of the van warm whilst your working
and as for water freezing on the glass, i've not had it happen yet even at minus 4 on a unheated conservatory,
sounds like you have lost the money already from what it would cost to go hot