it's still 9mm shy of BS guidelines though TJ and you're still going to get voids between the planks and the ply, but as I stated, somebody will probably be happy to do it but I don't drink enough horlicks :lol:But it's 6mm plywood as a underlay to the NMP, that would take out some of the undulations and make it stronger now and easier to remove in the future.
Sounds like a job for a collated screw gun.I'm gonna do it, with 18mm wbp screwed at 150mm, so that's 1,870 screws and use an S2 adhesive.