I run something similar on my F18. Except it is not in the boom and the mainsheet is trimmed from the mast / boom intersection. The nice thing about it going to the mast is that the crew handles the mainsheet all the time. When we tack, I can stay on the low side longer because I don't have to carry the mainsheet across.

The primary is very similar to Mike's. My secondary cascade uses a fiddle block at the mast / boom intersection and a ratcheting single with a becket that attaches to the primary line.

I'll try and post some pictures later.

I'd like to do run the cascade inside the boom, but I haven't found a light enough / large enough extrusion to do it efficiently. I haven't found one that is less than 1/8" thick which is a very heavy boom.

Mike, where did you get the extrusion?