Flat door are certainly far more common than curved doors.
With the exception of Airstream, every other RV door I've seen is flat. I like the look of Escape's curved door, but mine at least doesn't seal well. I think a flat door would seal better.
All of the early moulded fiberglass trailers had curved doors - Boler, Trillium, etc. Current models derived from Bolers still have curved doors, except the 17' model of the Casita line (smaller Casitas still have curved doors). Generally trailers that I've seen following the Trillium design (which includes Escape) have stayed with curved doors. Even trailers just entering production, such as the
Nest, include a curved door if fit with the curved body is important - the Nest has a curved door even though it is laid out like a Lil Snoozy and has the door in a nearly flat and vertical rear wall.
Most trailers have flat walls, so of course they use flat doors. Only moulded composite (fiberglass) and formed aluminum trailers (which means Airstream) logically have doors in curved body areas, so I don't think it's surprising that only those trailers have curved doors.
Cars are solid metal (mostly). This makes them rigid.
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I like the idea of a well sealing flat door.
It is certainly true that cars and trucks have much more rigid bodies, and that addresses the problem which I mentioned:
The important thing is that the door and frame match, and that's tough to achieve and to maintain in moulded non-cored fiberglass.
I like the idea of a door which seals well. Just making it flat would not make it seal, because the flat door frame would not stay completely flat any more than the curved door frame stays in the intended curve. Escape has a better-constructed door frame area than traditional moulded fiberglass trailers (such as my Boler), with the moulded inner frame section bonded to the outer shell. Apparently this isn't quite enough - or the door isn't stiff enough, or some combination of those - and being flat wouldn't change the situation unless it enabled the use of a reinforcing element such as an aluminum extrusion embedded in or fastened to the frame.
I don't think Escape will change their doors to flat but it would simplify production One 28 inch door for all their trailers with built in screen .They would have 3-4 hinges VS two ...
The Trillium/Escape door design - using those "refrigerator" hinges on raised pads - allows for as many hinges as desired. If it's just a hinge issue, an Escape could have more if the mounting areas were incorporated into the moulds.