I can't comment on the specific combination, but here are a couple of points: There isn't much difference in frame stiffness in a ford between '96 and '15. They changed it a little in '99, and the '15 is essentially identical to that. in '17, the frame got a lot stiffer torsionally.
They did change the cab height in '99, making it several inches taller than the prior years. This caused a lot of camper manufacturers grief. The '15 is again identical to the '99. However since the NL you are considering is a little newer than that, I assume NL has changed their molds to adapt (like Bigfoot did).
On an NL or Bigfoot, beyond clearance over the cab (which can always be solved by a simple spacer) there is clearance between the tailgate posts. These campers have molded bottoms, and widen behind the wheel wells to take advantage of the space. The clearance to the tailgate posts is low, like an inch or less. So measure that as well - if an issue it is not easily solved.
