I've discovered why I was having trouble installing the Climatology and Weatherfax plugins.
Somewhere along the line prior to attempting these plugin installations I had installed the OpenCPN program folder directly under Program Files (x86). Not sure why but that had been done.
Previously I manually created an OpenCPN folder between the Program Files (x86) and the OpenCPN 4.4.0 folder with the suspicion that was the problem since that was the default location for the plugin installation programs. The installations did not work correctly.
I have now uninstalled OpenCPN then re-installed it which created the OpenCPN folder between the Program Files (x86) and the OpenCPN 4.4.0 folder.
Both plugins installed correctly following the re-installation.
Sorry for the bother and thanks for the unnecessary help.