Coachmen made the house part of the motorhomes. Ford, of course, the chassis. Various other companies made many of the other components (appliances and such). These are not by any means high-end luxury units.
I've generally been satisfied with the quality of my 1998 Coachmen class C, for what it's worth; the fit and finish is not always superior, nor are the fittings anything above rental grade, but the workmanship in things that matter (like safe wiring, plumbing connections, etc.) is appropriately sound and the general design and layout shows some decent consideration and thought to usability and maintenance. It does rather predictably require more or less ongoing maintenance, as one might guess.