the problem is such a thing does not exist, answer is hard.
I am so happy with my storm but missing 3kw tank heater that would preheat the water before it heats the inline heater, but it is another cable. Two cables running into the van is a max I accept.
There is one option, good porty with heater on two cables (but not sure if these machines with two standard motors are good enough for at least 15m of hose run) and then get mytee air hog. Usually needed on commercials where we have better electrics or upstairs on separate circuit.
Porty with auto feed and auto empty while all switched on. Think that might be my next setup as at the moment I need to switch off the machine to empty and go the the van to fill the water.
So, for example enforcer 5.7vacs with heater + inlline heater + airhog.
Also water on the van can be pre-heated with up to 6kw heaters one the same cables when machine not in use, while you are setting up, vacuuming, prespraying etc.