Smee, the holes at the back of the unit dont meet up so i cut a bit of steel the width of the unit then drilled an 8mm hole in it so i could fix it down using the stud that is showing, 13mm nut fits on that. pull the unit down into place and drill 3mm pilot holes into the bracket threw the original marea holes on the sides. it wont move anywhere then. I can cut another couple of brackets if anyone wants them.
Walt, wimmy is gunna get the guide up asap but its virtually what smee said above. simple job really. should have done it ages ago