I build the housing so that it fits the side profile of the keyboard. Then I bolt it on. I use heavy bolts and washers and I epoxy it in place. The point where the housing is mounted to the keyboard is a stress point and I don't want it to break off or damage the keyboard so it needs to be firmly attached. If the surface where I'm mounting the housing isn't flat, I build a molded spacer that fits the contour and creates a flat surface to mount to.