Bralex, you're right, rollers are fun to do. If you have a fast roll rate, then you're right in saying that the timed application of the elevator works to carve the circle and maintain altitude. It really doesn't matter whether inside or outside, with a fast roll rate and properly time elevator inputs, both will work equally well.

What causes rudder to be required is slowing down the roll rate, and slowing down the number of rolls in the circle. The more time spent in the knife edge position, the more rudder is required to maintain altitute. A roller with, say, only three turns or two turns, (or even a single turn) in the circle requires the rudder to be equally as effective as the elevator in carving the circle and maintaining altitude.

There's a video clip of a 3 turn roller with alternating inside and outside rolls here: www.rcsites.net/tmills . Just click the plane picture of the Extra, and see what I'm talking about.