Ok another day lost waiting for a plumber but i did get the adjustable shelves in the van so not a total write off.
A few things ,I drilled the holes for the shelves at 4mm diameter instead of the usual 5mm so the shelf supports are a tight fit and dont vibrate out.
I used Pryda framing brackets attached the the cabinet and tek screws into the van interior to hold the cabinet in place at the top the bottom is sitting on the box over the wheel arch and is screwed down where possible,the whole thing sits up off the van floor as will everything eventually this will allow sheet goods to be carried laying flat in the back.The iload with the cargo barrier installed is only capable of a full 2400mm sheet at floorlevel up to about 250mm high off the deck.
It might not look like it but i have more items in the van than i have been able to carry before and i still have space available so once the fitout is complete this should work out pretty good all round.