Hi Jimmy, thanks for the heads up - i was planning on tilling behind it, unfortunately tilling below it isn't an option (long story but basically i need to be able to preserve the ability to access under it occasionally).
I intend to fit it on sectioned varnished ply (marine probably) to make moving it easier and 'just in case' - several tubes of clear Silicon stand at the ready for its assembly (I also intend loosening all the back plate fittings(e.g body jets) from the back plate and applying a bit of sealant round these to attempt to ensure a watertight unit - from your experience where are the hotspots for leakage?