Back in ’94, we poured a 17 x 67 ft RV pad (13-15 yds concrete) on the side of the house, complete with privacy fence, motion-sensor lighting, boat swale, sewer, electricity and cable JUST so each set of parents could bring their motorhomes for a few of the “cold” weeks per year and live with us (instead of the nearby KOA campground). Due to illness, the RV’s never came to try it out. They all died between ’95 and ’00.
Even the best intentions end up being for naught, sometimes. That’s how life is.
UCGal, from your posts, the Piggs know all the headaches and expense you went through to build it for them. If you just can’t get your in-laws to stay there anymore, and your guest house is separately-metered, maybe you will be able to rent it out to a quiet UCSD student or senior citizen.