The problem described in the initial part of this thread sounds a lot more like a frame failure than the typical rear-end separation common to the 70's era trailers. Good news is, that your frame probably can be repaired/strengthened (which will only require digging into the belly pan) without as much labor and trouble as repairing a separation (which would require removing the interior furnishings and skins in the back).
The bad news about frame droop/failure is that towing for hundreds of miles to a place to have it looked at could cause even more severe damage. Another option may be to look on the "portal" page and see if there is a forum member who volunteers to do pre-purchase inspections in your area. If you could get someone with the properly "calibrated eyeball" to check you out, at least you may have a better idea of what the real issue is and how safe/unsafe it is to tow. Then again, most RV places ought to be able to spot a broken frame--you probably don't have to take your trailer to the mother ship to get this repaired.
You might also contact Area 63 Productions (http://www.area63productions.com/
). They are a custom Airstream repair/rennovation shop that might be closer to where you are.