I've actually seen more rolling harrier inside loops than normal rolling loops. You see it in 3D with the guys that really fly it well. I saw Frank Knoll doing them at a Fun fly near Chicago last summer with a 40% (Great planes Extra 42% I think). He wasn't even going more than a 100 feet off the ground at his max altitude. Something to see.

One thing I like to do is square inside loops with a roll in each leg. Very fun. For an extra rush tighten them up as much as you can.