I suggest using
Hamachi with RDC. It's a secure P2P VPN app. You install it and are assigned "permanent" (on Hamachi's servers anyway) addresses in the 5.x.x.x subnet. By doing this you:
1) Don't have to worry about your ISP changing your address, b/c you're connecting to the Hamachi 5.x.x.x address
2) Encrypting your remote desktop connection sessions
3) Don't have to worry about forwarding any ports. Hamachi's servers initiate secure handshaking from outbound connections, then bows out.
It's really one of the coolest applicatons to come out in a long time, IMO. It requires almost no configuration. If you end up looking into it, I suggest you run the installation simultaneously on all machines you want to connect to. Since you're assigned a permanent address, if you install simultaneously you have a better chance of getting concurrent addresses.