I have a Tower of Portals, two Stories tall so far.

In the middle is my Castle Portal.
Surrounding that, are portals in every direction.
All portals must link to this Hub
The only way inside this Tower is via a Portal
And there is only one set to go from Tower to Castle.

This is the best setup I've managed so far, as Dialing Out became tedious and time consuming. Though I still like to imagine I'm Dialing Out like SG1