Hello Carl,
I tried to use a VPN for the remote rig and I did get it to work, however...
The VPN keeps track of ALL the data to ensure that the data gets to the other end. The result of this is that if the link goes a bit slow, then the data rate is slowed but the VPN does not get rid of any data so that the voice data is also slowed, but a PERMANENT delay is introduced into the voice, which make it useless. This may not happen all the time but when it does it is very frustrating. Further problem is also that the control is also delayed.
Thus, if you do not need to use the VPN then use port forwarding at the remote modem.
Good luck.
Andrew
VK3OE