Tough question since quality can always be improved with time and money, neither of which are given out readily. That being said, I think most of the quality complaints can easily be solved given a dose of these. Boiling it down to a couple of areas:
1. Water leakage (which causes delamination and wood deterioration. From what I can tell trailers are being built much they way they have been since the 1965 trailer I am restoring. Sidewalls but up against each other and roofs, are jammed with putty and covered with metal strips. Also roof seams and penetrations are generously gooed with caulk. There are better ways, but right now the easiest way would be the generous use of some strip sealant like Eternabond. I think this would eliminate leaks and about 75% of the complaints.
Next is floor structure. Either the sandwich foam structure of just a sheet of OSB. Two thoughts. My 1977 Jayco PUP had a plywood floor exposed to the bottom (no insulation,just an undercoating) and it held up with no rot in the 31 years I had the trailer. The 1965 trailer I am working on has a plywood floor, had fiberglass insulation and sat on a Celotex siding (1965 homebuilding product) that was exposed to the road. Again I saw no rot on the plywood or wet insulation. Only problem with the floor was in the corners where the edges leaked (see item #1).
Finally is general construction technique. Most trailers, cabinetry and the like are assembled with an air stapler and framing lumber, like 1 X 1 covered in paneling. Again, time and money would fix this.
Obviously there are a lot more but you get the idea.
JU