You don't need a VPN for overseas access. Unless you specifically need it? I simply set up my slingbox in my network as the only IP address visible to the outside world.
When you set up the slingplayer on your home network, the software locates the unique identifier for your slingbox. When you then connect from outside your home, it uses that identifier to connect to the slingbox, and you are then able to watch streaming TV,
My brother uses a slingbox in my lounge to watch UK TV from overseas. The only limiting factor is your upstream bandwidth.
Slingboxes are a doddle to set up. You download the software from their website and it configures the Slingbox. If your router is UPnP, it will open the correct port on the router for you, but the software will tell you which port to forward if you have to do it manually. Each Slingbox has a unique number and when you set up the box, it registers to their servers, so the software can always find it, like a VoIP setup.
I have the Slingbox software on Windows, Macs and my iPhone and whilst the video is slightly compressed when viewed over a 3G network, in order to be able to stream successfully, I've not had any jitter or dropout yet.