Finally got the truck, next will the fifth wheel fit ?.

It will be close, as to the B&W handle hitting the box, not to allow release of jaws?? Another brand hitch, Reese, Curt, others, may work?

While you'll want to have at least 6"s of bed rail clearance, which may clear top of tool box, most situations, there will be times it could be an issue.

Comes down to how bad you want that tool box?? Might work/might not? Could you change out to a smaller box, if needed? The tank height shouldn't be an issue.

Jerry