In pulling the bottom skin off the 72 29' Ambassador I find the reason for frame droop behind the axles. Under an aluminum patch I find someone has jacked on the curb side frame at the rear of the plate the axles bolt to and have bent the flange of the channel upward considerably for about 6-8 inches.
The frame sag is greater on this side. Have not gotten far enough to see the other side well. Got rained out.
I suspect that some of the wrinkling of the flange is as result of the frame bending after the damage was done.
In the process of planning a repair at this time. Still have not found a copy of service bulletin that supposedly addresses frame repair in this area.
This find does perhaps explain why pre-greywater tank Airstreams have frame sag behind the axles.
The morale is, be careful with your jack.
Dan Phariss