I'm not trying to pile up the posts -- just want to help quickly. Gotta move my just winterized '06 Safari from the driveway back to storage. See this link: http://www.vintageairstream.com/rr_t...condition.html
There are no hard and fast numbers. I'd look carefully under the gaucho to see if it looks like there is any dark or rotten plywood under either the front or back of the water tank -- most likely from the windows, not the tank. Is the back shell well caulked at the rear bumper? Does the battery compartment seem real intact and solid? Take the battery out and inspect tray & caulking under it carefully.
Does the A/C work? Only use a 30A circuit (like in a campground) to check or else it could burn out the compressor. Have them start the fridge one or two days before you inspect it -- it'll take that long to cool.
Best wishes -- and let us hear about your results!