Great minds think alike! We are also looking for a "shell" to use as an office, first at the site while we build our house and then as my telecommuting office. Someday might restore it for travel.
My limited research has taught me that we are looking for 24-26 feet, thus a Tradewind, Caravanner, or Overlander. We want double axles, and it has to be watertight, i.e. no tree landed on it (!).
I avoid looking at the ones with really nice interiors, as they are beyond our budget and we need the space for desk and storage at this point. Ditto for plumbing, although I would be very happy to find one with working electrical.
Where to look? The classifieds here, ebay, and a few other nationwide classifieds, but personally I'm concentrating my search locally. That way I can go look at it before buying, and it won't be a long tow to get it to our property. I live in a rural area, so local means anything nearer than a 3 hour drive. The trick is finding out which ones are actually for sale. I look in the paper, listen to the radio community announcement programs, etc. I haven't posted any flyers yet, but then we aren't in a hurry either.
I'm also just starting my search, but I hope this helps. We both probably did the smartest thing by signing onto this forum.
Best of luck!