My non-Airstream, 1984 vintage travel trailer has an aluminum roof--but no internal deck on top of the roof framing members.
I am patching a hole in the roof about a foot from the rear. PO gobbed silicone in the hole, but I will patch with sheet aluminum & seal the patch with Eternabond. I have not opened the roof from the outside and do not think that is necessary (but I could be wrong).
However, from the underside I see that the aluminum roof has about a 3/4 inch gap to the upper surface of the curved frame crosspieces. The gap is cause for low spots on the roof at the rear of the trailer.
I am wondering about filling in the gap with strips or slats cut from 1/4 or 3/8 thick plywood or Oriented Strand Board (OSB).
Another possibility is to cut strips from a rigid foam insulation panel.
Looking for ideas.