Hi Nego_O
I mounted mine (y axis) by attaching them to some slotted aluminium plate and then attaching the plate to the torsion box under the machine via some self tapping button head screws throught the slots so they were adjustable forward and back by about 1/2 inch. I could then easily set them up exactly where I wanted them to trigger.
The screws are rock solid in the MDF. (You can also overdrill the holes and fill with epoxy before putting screws in. That way they are treaded into the epoxy not the MDF)
Hope this helps