Ok, I live in a county in Indiana with a large Amish community a couple hours south of where most trailers are manufactured. I can tell you there are some fantastic Amish craftsmen but they don't build RV's.
The RV industry is like every other industry in the US. They want the cheapest labor that will show up for work and then work them as hard as they can. The young Amish men fit the bill pretty well though they aren't the majority of the labor force. Many plants have covered stalls or small barns to keep the horses during the day.
The majority of the work force was Hispanics until immigration tightened up but they still serve a large roll. If you spend any time in a RV plant and I've been in many of them, you will see some very hard workers. Many have no more than a 7th grade education working their buts off with a screw gun going as fast as they can. When you work them that hard in non air conditioned and poorly heated factories you get the quality that we all complain about.
Sorry to burst some bubbles but once again profit is more important than quality, that's why the Amish craftsmen work for themselves not corporate America.