Hi Daz
Most I have seen, have been hard mounted but it wouldn't hurt to use some AV mounts, i'd keep them on the firm side though.
Seem to remember reading in the manual that it was best to try and mount it well away from the heat of the engine bay
The vibration problem relates to the Megasquirt system, the one that has a daughter board fitted ( This has been known to work itself loose )
All of the Megajolts components are hard soldered & shouldn't vibrate loose
