My ’72 has the same condition. The rear end and frame is solid as well.
I had water leaks and the floor would be damp after a good rain. I’ve repaired all the water leaks but the damage has been done.
With everything sitting on top of the shower pan it looks like it will be a major project to remove everything to inspect the floor. I’ve contemplated dropping the belly pan and seeing if I can assess the damage from below.
Got outer things to do higher on the list.
AirForums # 2806
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Avid supporter of trailing edge technology.