Since it is a "sticks and staples" type of motorhome on a truck chassis, and after confirming the front end alignment and/or rebuild, maybe you could look into one of the aftermarket steering stabilizers offered to the RV market like this one from Roadmaster
http://www.roadmasterinc.com/products/rss/reflex.html
Also, I have been reading articles in the FMCA magazine about S&S type of motorhome suspensions bring overloaded right from the factory, it may have a broken rear spring, or worn out already bushings, get it on a rack and look under it really well.
Take a quick look also for Converted Busses, for $30K you could find a really really nice Conversion on a chassis thats made to last a Million miles, built like a fort, and returns many smiles and random "thumbs-up" wherever you go!
Mike Siebert F421097
Portland OR
1948 Gillig