i might have sourced some EBERSPACHER HEATER's
they are original german MOD type, small and compact and run on DIESEL and are 24 Volts
Im just about to secure them (i think)
the only issue is, the fuel tanks ( i plan to use Bike fuel tanks for the diesel, if your van is diesel then no probs) and the 24 Volt, i have a guy working on this issue, he says it shouldnt be a major expense
i will post when i have it sorted, for any1 in the know, EBERSPACHER are the dogs danglies of lorry / night heaters, then run for hours on 1 L of fuel and last for ever