I did some work on fiberglass siding and when it cracks, you can buy mushroom trim to cover the joint. Done right looks like factory thing.
With delamination, I was able to pull fiberglass panel out, clean rotten plywood from it and reapply to new plywood on the structure. Takes some boards and holders to glue it flat.
I had aluminium siding on 1980's RV and at the time manufacturers were using corrosive glue on them.
Meaning the siding was corroding from inside, showing blisters outside after few years. From my observation the issue was not corrected for decades.
