Unfortunately, I do not have any screenshots or any worlds with that build - I had a corrupted HD that caused me to lose a lot of stuff. I'm working on something like it now though, so perhaps in a week or so I'll have something to show you? :/ Sorry I can't be of any more help visually, but I can still describe what I had going in perhaps a bit more detail:
I generally leave an open square in the very center of the base - on a 2x2 (chunks) fort, it might be just 6x6 (blocks), but in a 3x3 (chunk) fort, I've gone so far as to leave the entire center chunk unfilled with anything. This allows pretty open access to all floors, assuming you have a means of flight. As a backup, I also (in my most lavish fort) used a bank of IC2 teleporters that sat on the edge of each level of the hole, so that if I had no power-suit power, or if I had somehow died int he overworld and didn't have a means of flight, I could use that. As an even further precaution, I had a mostly hidden "emergency stairs" stairwell that ran down one of the sides of the fort that I could use to travel manually in the event of a complete power blackout (it never happened, but I like to be prepared). I also kept a chest in that stairwell that contained, among other "emergency" things, a basic jetpack.