Yup, the majority of sewer hose couplings don’t fit in the tub on the NL campers. The one they supplied does fit but man is it tight....
I have a 10ft hose with the supplied NL coupling and I use a Rino elbow when in a RV park which easily threads on the other end when needed. I keep that rino elbow / coupling in a large zip lock bag in by the valves.
Buddy of mine is a welder / fabricator. He’s looked at it and figures if they just added a small section or ( 1.5 inches) of 5 inch square stock with a bigger 5 inch door, that would solve most of the problem with one end.
If NL made the entire box 5” they would have to also modifie the back landing as it is only as wide as the sewer box tube at ether end.