fitting a 1000l ibc in that van is stupid beyond belief
with a 500l tank full on board it will be overweight, have you not read the posts on this forum? with a 900l payload 500litres puts it the van on its limit,
I dont think its a good van for a 2man set up, it doesnt have a payload good enough and its too small, you need a minimum of 1000kg payload for 2 men, ideally 1200kg+
was it 12000 including vat? or are you not vat registered? if you only use a 250l tank between 2 men I'd go to a 400l then you might be not overweight when full