As Andy say's it is not quite that simple.
I found out many years the hard way

I was reading in my Hymer manual and it said something about UNLESS travelling with the heater on

This made me think that I possibly could

It had snowed and we had solid ice on the roof so I left the heater on and I did not get a mile from home (at under 30mph) before we had some sort of blow back

with evaporated water like a mist blown from the fire (heater) across all of the inside of the van

Cost a few quid to sort out as the local dealer did not believe what happened and he was looking for the wrong fault

Towtal say no more

Our present Hymer has a factory fitted heater under the dinette which works from the hot engine water going through a fan heater.
It is absolute perfect

and we never need to have it on more than a low setting and we are greenhouse plants

The other option is a diesel heater, these also can be used while driving.
Both of these are much safer than gas, (my opinion)
