Yeah, I feel your pain... See my post here titled "airstream quality control". Or just do a search re: Pepsi under the member search or post search to view it....
I found the same thing, same problem. I painstakingly removed all of the OSB from the frame and master cut the plywood to fit in and around the frame screws, which are critical to the structural integrity of the unit.
You could put your finger through the floor, I pulled out chunks and clumps by hand. Black and moldy. Our problem originated with a poor wheel well design. There is a seam between the wheel well and the frame doomed to fail. I have a fix for that too. Rivit or screw on a metal shield over the crutial part of the seam, the front and back. Then, spray on bed liner. I think we are going with Line X. You choose.
We have two Airstream trailers. one 1975 Trade Wind and one 1994 Excella. Both 25 footers. The 1975 has good solid ply wood. The 1994 has OSB. I have heard roomers that they are using partical board in the newer ones. Funny thing,
the display I saw at the AS dealership in Sacramento had 3/4 in ply wood, not OSB, not partical board. Seemed like false advertising to me...
We are at firstname.lastname@example.org
if you have questions...
We had both our trailers in Yosemite for a shake down cruise after renovating each of them with new floors, servicing all components and new upholstery. They worked GREAT. Love em.
Airstream made them. I made them better. It will take them much longer to rebuild my opinion then it took me to rebuild their trailer. My standards are high and I would own no other. I just want Airstream to maintain the Quality Control, so that we, the trailer owners can maintain their reputation.
Happy travels all.