OK...done, everything is working now :)
Sometimes it's the simple things which take time to figure out. (That's my story anyhow.)
I traced the power feed that goes into the converter board backwards up under the hood. It terminated in what I believe is a fuse link (the kind that resets after it cools.) There was continuity across its terminals, so it was OK.
Following the next lead out of that fuse link the cable went to a solenoid. It had continuity across its poles as well. The cable out the other side of it went directly to the house battery.
Sure enough, power in that cable, but not in the cable out of the closed solenoid. Poor/corroded cable connection on the power side of that solenoid was the culprit. Disassembled, cleaned and re-torqued and all is now well.
Guess all I can say is that I'm happy it all works now and I've learned a bit more about my RV. Otherwise...**** frustrating!
Thanks a lot to those who posted along the way here. The input was much appreciated.
