mathew - can i make a massive safety suggestion.
move the tank to the front of the van.
I know its a lot more convenient where you hgave put it, but the first time you go round a roundabout in the wet with the tank full the chances are that the back end will kick out, don't forget, when full that tank wieghes of a quarter of a ton and not only needs to be secured right, but also positioned properly.
Justin Ferrell
Cleantech