Thought i was going to be way over with all the additions fitted , heater , gas bottle , solar panels on roof , 350 tank and frame plus power reel !
Turns out with a full tank and everything i need to carry i have come in at 612kg , payload is 610kg .
As long as i dont get stopped before the first 2 windows im laughing 
that picture you put up a while back of your van Rich i thought you had an elephant in the back! ;Ddoes your back tyres not scrape on the wheel arches?
i think your crazy using a little van like that for wfp!
Yes , It does sit a little lower than i would like , but nothing fouls anything , and when i get down to 250 L it comes back to normal ride height .
I took the step of putting increments on the sides of the tank while i had my gear out so i can monitor my usage , most days i come home with near 100 L i reckon , only 2 days a month i get close to running out .
I am looking at putting my 250 in and having the backpack and 1 barrel full , that will put me at 300 L which will do me apart from the 2 days i mention .
So i will split the day of half a million gaffs into 2 days and top up with low usage jobs .
The other day is commercial and has low TDS water on site , so no problem .
This will knock about 55kg off straight away .
As you say with regard to the van being too small , yes , looking back maybe a Berlingo or Doblo would have been a wiser choice but i have been on the other end of the scale with a T4 and all i did was carry lots of stuff i never used !