well, we have a keystone outback, 2011, have put over 30K miles on it, put ove 100 days camping on it each year, including grandkids in the trailer.
The only issue we had with it was the clearcoat on the alloy wheels cracking for which keystone replaced the wheels, paid for balancing etc.
Daughters in-laws have a keystone cougar 2009, they have probably 20K miles on it, 60 days/year or more on it and again no problems with it everything is holding up well, both look almost new inside.
Now the in-laws trailer is stored outside w/o a cover and the decals are starting to curl. Ours is stored ouside covered whe not in use for more tha 3 weeks or so and the decals are still in great shape.
Both of us would by another keystone in a heartbeat.
BTW Thor owns airstream, and probably makes well over half the trailers sold.