Hello,
this may be of no interest - I am aware this is a cycling forum - however according to the scaremongers this winter is going to be bad (I know it always is). I still go take the bikes out in the van sometimes to go for rides, and often in winter you can get stuck in jams etc so I thought I'd just put this here in case anyone wants to do the same as I have.
Regular electric heating solutions are pretty useless off a 12v battery. I managed to acquire a cheap second hand eberspächer hydronic heater for £50 which works perfectly well - I plugged it into the coolant system and now the standard van heating vents etc give warm air with the engine off. This uses hardly any diesel (or petrol depending), and won't kill your battery instantly like any electric heater.
In case anyone is worried about being freezing cold and stuck on the M8 (as I was a few years back) - and is at all interested in doing the same thing, give me a shout and I'll tell you what's involved...