Answer from someone who has run countless slip tanks both steel and aluminum.
Your fears about either material is 100% unfounded.
But you can get a plastic tank if you can’t get over the fear. However they are generally like the Fischer Price version of a time tested tool. In certain conditions I’m sure they’re fine and may offer a couple small discreet advantages like easily moveable or transferable between vehicles or locations. even though folks who probably profess to be safety conscious somehow have no issue with a large quantity of unsecured fuel container in the back of their truck.
And I’ll answer a question with a question. If a dedicated diesel tank for the truck, why the aversion to plumbing it in for hands free operation?