this may sound...dumb but as far as sag in ones with a rear bathroom...you mentioned if you could get a pencil between the body and the frame that was too much....exactly where do I find this..is it under the home where the bottom plate meets with the shell?
There are two separate issues that may be present in Airstream and Argosy trailers. One is separation and the other is sag.
Separation is one that is most often present when the coach has uncorrected water leaks resulting in rotted flooring, and/or when significant loads have been carried aft of the rear axle (such as a rear bumper mounted spare tire). This condition can be identifed by monitoring the amount of movement between the body of the coach and the top of the rear fram rail where the body should be resting on the frame rail - - when pressure is placed on the bumper, the bumper should not move independent of the body (in other words a gap should not open up between the body and the top of the frame rail). My '64 Overlander had this problem, and the repair was to install "gallusses" or suspenders that reattached the body to the frame at the rear (the repair can be identified by the existence of one or two rows of extra rivets on the body of the coach running from the top of the rear frame rails up the rear body panel - - there also may be small patches covering the access points where this repair is made.)
Sag is a problem that is evidenced by body damage on the sides of the coach just behind the rear axle. The cause(s) have been listed as running with unbalanced running gear, or running a coach with full or nearly full holding tanks on a regular basis. The repair for this condition is typically the installation of frame reinforcements in the vicinity of the axles. Such repairs can usually be identified by "elephant ear" patches in the vicinity of the area reinfoced. The problem can be present in virtually any of the longer Airstreams, but was more prevalent in the earlier 1970s coaches.
Either of the above problems can cost in excess of $1,500 to have professionally repaired.
Second deal...does it take 2 to set it up or could one handle it on trips.???
You would be among friends as a Free Wheeler with an Airstream. There is an Intra-Club within the Wally Byam Caravan Club International (WBCCI) that is composed of Airstreamers who travel alone (Free Wheelers). There really isn't any aspect of RVing that is particularly difficult for the Free Wheeler, it just takes a little more planning and preparation as only one person will be responsible for all aspects of the travel experience. In my experience (after Free Wheeling for more than 20 years), a good "Hitch Helper" hookup mirror is the most valuable accessory in the Free Wheeler's tool box.
Good luck with your inspection and decision!