Brian, Thank you for your response.
The settings on my router were different than your suggestion, but I was finally able to access three linux boxes from the outside. My settings were
external port 5900 forwarded to static IP addres 192.168.1.17
external port 5901 forwarded to static IP addres 192.168.1.18
external port 5902 forwarded to static IP addres 192.168.1.19
All boxes listen on port 5900. Not sure of exactly how the signals are routed to the boxes.
I found this suggestion in the following link:
However, I am curious about your approach and will try it.