to revisit this one last time, (promise!), any reason I cant re-deck with 22mm P5 and then overboard this with 12mm WBP? Reason for asking is it will be less critical to get the noggins in the right place to support edges of the ply, the P5 of course having T&G which I can glue.
If noone thinks this is a bad idea then this is the way Im going to take it......