Hello from Colorado and welcome to the vintage Airstream hobby. You're 69 may have some fiberglass parts as opposed to all ABS plastic stuff like my 75 has. Your suspicions are likely correct, you will find cracks in the bath parts. But they can be repaired to be better than new.
Here are a couiple of photos of my bath as I took it out, and then put it back together again with new plumbing and wood supports and the like. The plastic bathrooms in these old Airstreams take some time to make good again.
This is a rather old thread and might not garner much response. You might like to take a look at the Airstream Trailer Knowledgebase near the bottom of the Forums page, then select Sovereign
, and then select your year range. You can see how folks worked their bathrooms. The model year 1969 was the first year of the new body style. The 68 was completely different. But model years 69, 70, 71.72 were very similar in construction.
I disassembled the bath completely, repaired the rotted floor in the back of the bath, painted the plastic parts, installed new plumbing through the trailer, and then put the whole hot mess back together again. Keeps a retired guy busy.
Hope this helps...