Thanks for the reply folks.
As I mentioned in my original post, I won't have any allocated parking so putting a heater in the van (as I currently do) isn't an option. I don't have the filters in my van so that's not an issue, but taking the reel and pumps out isn't an option either.
As for the hot water running off gas/diesel...how much noise would these options make? I ask because say a van is parked on a road and it's making noise in the middle of the night, firstly, is it going to disturb anyone? And secondly, it's going to attract attention to it from the wrong sort of characters, so a break in would be inevitable I'd imagine.
Any more thoughts or help would be most welcome though.
I'll look at the links at the insulation options.
Thanks
Jamie