Buy the rig that has been maintained the best. A motor home is more complicated than a car - it has two basic components - the RV stuff and the car/truck stuff. An RV mechanic tends to be good on the RV stuff but not so great on the auto/truck stuff. If your concerned about the car/truck stuff arrange to have a mechanic check it out.
If it were me I would have a mechanic check it out. Also - biggest risk of older rigs is that they tend to leak. I would have the rig pressure tested to insure it isn't leaking - that cost about $100.