New or used...they all have problems. Always have.
I own a Grand Design unit, touted to be one of the highest quality builds out there. They are not! Same issues as other new units.
New trailers are pieced and slammed together as fast as possibly, no matter what the brand name states, using the many of the same major components. Often its the components that fail, not always a build quality issues caused by the name on the trailer.
What you pay for buying new, is getting an unmodified trailer with design and colors you personally prefer. (And of course no one else has lived in it!) Buy used if you want to save big money but compromise on your preferences and anal details.