@Y100 just as a balanced view, I don't have a diesel heater, I have a space reserved for one and a vent space allocated in my camper....
As a DofE instructor I often camp in hiking tents in January so am fairly hardy to cold conditions.
However when it comes to the camper in winter I am usually on a campsite either in the UK or French Alps. Therefore I will have electric hook up, so I use a small oil filled electric radiator, this I can leave on 24/7 at no extra cost to me (no diesel consumption). Pick one up at Dunelm or similar for £20-30.
Heats the van lovely and keeps it warm all the time. Obviously it has a downside in that it can only be used when on mains. That's why I have left the option for a diesel heater later, but at the moment I'm living very comfortablely without one.
On the odd time I wintercamp off grid I just take a down filled sleeping bag and I'm normally toasty in the van.
Just giving you an alternative view, the diesel heaters are great, but I have to justify the £900 against £30 and a £5 charge for the electric. Either way, just get out in it this time of year, I'm watching
@Salty Spuds post and very jeleous of him out in the snow.