Before I tested the solution:
I do have the 40 terrain entries added as instructed. So that checked out.
I see ORBX!OPENLC_NAMERICA1 and ORBX!OPENLC_zBase as well as ORBX!LC_Europe1, so if I understand, I should have Tongass between that group and the ORBX regions and airports - yes? I'll try that. When they look dark green all in a bunch with Lorby, I just didn't recognize the look of it.
I do have Tongass higher over the lower, so that checked out.
I didn't use the xml method, but thanks for your 2b - others may need that.
After I inserted both Tongass higher and lower between the LC's listed above and the ORBX regions, the result was...water disappeared again. Didn't work. I must be missing something.