Hi,
Well we talked to many people and this is our Opinion on it.
We will use Alu or our Airtanks, our Box is made out of Alu and some other small items.
Diesel tanks will be out of steel. Mainly because it is easier to find someone who can weld steel then Alu. So just in case. Our Boxframe ist also out o steel, same reason would be the welding, but the main one was that it fitted and was on the box.
Mike