Another must have that I don't think has been touched on, is a balanced trailer.
Of course, manufacturers can't figure how owners are going to load the trailer, but they can figure where heavier items typically go. Fridges and pantries should be near the axles. Front pass-throughs are good....as you add weight, so does the tongue weight increase.
I realize you can't put everything over top of the axles, but 3 items need extra consideration........all of the tanks. In a rear bathroom, the waste tanks tend be directly under the rear (oops, pun intended
) of the trailer. If the owner needs to travel with the waste tanks full, weight is taken off of the trailer tongue while weight is being added to the trailer.....not a good situation. Granted, people rarely travel with full waste tanks, but it can happen, especially with those choosing to boondock.
A mid-trailer bathroom, with the fresh tank, gray and black tanks directly in front of the axles would allow for better balance overall. And aiming for 12% tongue weight with a battery and propane tanks coming off of the factory floor would be another big plus.