Finally installing P3Dv2.5
Success!
So far, so good. I did have trees in the water after initial upgrade to 2.5, but then I remembered this thread. I had a copy of terrain.cfg from before, so I deactivated the new ones, and pasted the saved one in both spots.
Eureka! The trees are gone. My boat is floating again.
Before starting the v2.5 installer, I deactivated the 2.4 P3D.exe file by adding a ".off", then ran the 2.5 installer right over my current 2.4 folder. All scenery is intact, and a new library installed.
I've also installed the version 2.5 SDK package as well. Now I need a new Instant Scenery III dll update.
Checking out the AI Shipping in P3Dv2.5 - Look who I found!