I did it the old fashioned way: cut the rough outlines with table- or bandsaw, then filed (and sanded) the parts to exact fit. And i can't recommend it to anybody, takes forever!
I wanted to keep the propulsion part modular, so I used up a lot of time cutting out all the little notches and square holes, instead of simply cutting square pieces and cementing them together. This gave me an insight into the thought process behind the OpenRov.
Besides, I somehow ordered slightly bigger props and had to modify the prop guards for a bigger diameter and redesign the handle/support brace parts anyway.