Yeah, False ribs would be perfect, but hard to do in an ARC. Can be done, though: cut the slots through the bottom sheeting down (up??) to the top sheeting. The hard part is making the template - I just made a 1/2 template using the exposed bottom, then used it to make a ful sized cardboard template. I think going spanwse is easier and seemed to work fine for me.
The 1.20 2-stroke should be plentyofpower!
-Will