I forgot to add that mine has the upfitter switches for accessories. I put a 91 gallon fuel tank in the bed with a pump that I can refill other stuff. The tank has a gravity feed into my truck's tank that work great.
The 12v DC pump has an on off switch and it is supposed to be wired directly to the battery. I wired it through a relay and used one of the upfitter switches on my dash as the master on/off. This reduces the likelihood of someone stealing the diesel and the pump somehow knocking itself on or something.
One of the dumbest things about these trucks is that they come with a cap less fuel tank. You can get a nice magnetic cap for about $16 and it keeps the dust, dirt, and accidental splash of DPF over into your diesel tank. They put the two fillers next to each other and this isn't one of Dodge's better ideas.
I don't like the idea that the door isn't lockable either. I wish I could put a locking cap on it, but I haven't found one. You can put a locking filler door on a 2500, but they don't make one that fits right on a 3500 dually. You will at least want to get the aftermarket cap for it.
