Hi Rog,
I have a combo 775 kg epic van, it has a 400ltr flat tank, merlin ro, di can, 100 mtr micro bore, 25 ft & 12 ft predator, step ladders, ladders, trad gear and me (80kgs). I have had it all on a weigh bridge with 350 ltr water and it comes in at 663kg.
Hope this helps. It carrys a lot more than an astra van as I used to have one and it was only good for 250 ltr.
Cheers Jason