Guess I'll jump in here as well. I've had three fifth wheels, all of which have had Lippert frames under them. The first unit had pin box flex problems. I was one of many and fortunately, my pin box did not tear out before I had a structural engineer design a retro fit kit to strengthen it! That said, I did have the camber go out of one frame I beam, which caused a weld to break inside a wall. The repair cost over 18K and required the beam to be cut, jacked back into spec and a plate welded over the cut!
When I contacted Lippert about the pin box flex, they indicated they just build the frames to the manufacturers specs. I asked if they had engineers who checked over the plans and was told no. It is a manufacturers problem. In other words, pass the buck!
My second fifth had so many other warranty / quality related issues, I did not own it long enough to have frame problems, although after two years, I had to replace the tires, as the axles were out of alignment and caused premature tire wear!
Now I'm on my third, a 2014 fifth wheel. While I have not had any frame issues yet, I know of several people who have. Recently, I had the MORryde SRE4000 suspension system installed. In preparation for that, I designed up two additional frame cross braces. The trailer was designed without any! While installing them, I found all four of the spring hangers to be welded seemingly anyplace close to where they should be. I had to make individual shims to take up the space, as much as 1/4" I don't know how they expect to align the axles, but I'm expecting to see tire wear quickly. I doubt complaining to the manufacturer, or Lippert will cause them to agree to cut the spring hangers loose and reposition them. More than likely, I will have to find a frame shop locally that can do that work.
Bottom line is there is no oversight in an industry that produces a product that we pay high prices for. It is sad true fact and the ability to trust in a quality product coming from them, no matter who the manufacturer is, really is not there. It is a 50 - 50 chance that you will get a unit free from "defective engineering and workmanship.
Bandaid