Sounds like a potential keeper but plan on replacing the tires very soon. You can use that as a negotiation point to get a few $$$ off the price. Regardless of storage and low use the power train is still going to need servicing if it hasn't been done based on time. Engine and transmission oil, brake fluid change, there are 13 or so grease fittings on a Ford front end (if that is the chassis). Are the chassis and house recalls up to date if applicable? Does the owner have maintenance records. Big bonus for you if they do.
You want to run everything on the house side. Roof ACs, furnace, fridge, water heater, TV's, dash radio, everything. Coach and engine batteries might need replacement due to age so negotiate on those items also. How was the movement of the slides? Same with the jacks, awning, steps, microwave and generator under a full load. How is the view the rear camera provides. Is the camera foggy? Any possible problem you find use to your advantage getting a fair price.
Pull a CarFax just to be sure it wasn't in a flood or other such disaster. The report will probably show nothing more than yearly registration but doesn't hurt to check. Saw a couple of very nice rigs for sale post Hurricane Sandy that were in water up to their floor. Insurance write offs but clean up well. Potential electrical problems down the road will make your life very difficult.