SB - i usually have them on ( via timer ) from 11 pm thro to 7 am so most of the electric used is on 'cheap rate' :
i've only used them the last 3 weeks since it's got below 10 degrees
yes it takes several hours to get to this temp but it's doing a dual job as it's stopping the van freezing up so saving
me putting in a heater for the night.
for me it's a great choice as things are not clear on the use of/having LPG in the van, 1 don't need to cut a hole in the
roof nor do i need to work with the doors open due to fumes being produced.
i could not go down the immersion route as the tanks are bolted into the van and no room to drill holes in the tank where
for access and i would worry about doing it badly and i think the less holes in a tank the better.
i currently just drop the heater and powerhead in through the lid - no mess no fuss takes around 1 minute to deploy and the same to retrieve in the morning
i would at some point splash out for a pro system ( pure freedom ) that is diesel but as i posted earlier my biz does not warrant that kind of luxury
Darran