I have a 2007 373ds. I bought it 3+ years ago with 10,000 miles and have 16,500 miles on it now. I have had no problems with the side wall. A good road test with someone else driving and you in the pass seat watching the sidewall and floor will let you know if it has an existing problem. The problems I have run into have been minor except for replacing the upholstery. ( did it myself with replacement covers from Williamsburg Furniture ). Minor problems have been the rear sway bar bushings were shot when I purchased it. Water heater anode was bad occasionally causing the toilet flush valve to clog. Replaced the hvac thermostats with digital. Replaced the radio speakers. The dvd player went bad so I just replaced it with a cheap household one. Replaced the bedroom tv with a digital one. Also had rain water get into an outlet which was mounted in a side compartment just forward of the right rear wheel. This caused the gfi receptacle in the kitchen to continually open. Other than these problems she has been great. I do have the headliner coming loose throughout the coach but this model has many items attached to the ceiling that actually help hold it in position. No where does it sag more than 1/2". Hope this helps you make a decision.
Paul.