Why not put a heater in the Storm tank, have a duel switch on vac 2 so either the heat is on or the vac, this will keep it down to 2 cables from the machine. Pre heat a tank of water while you prep and then use a magma nearer the wand. When I used an in tank heater I just kept it topped up so the heater could keep pace. I personally would put immersion heater in a tank in the van and heat that before leaving for the job, with insulation it should keep hot for ages and then an inline heater nearer the wand.