OK, I flew the dreny with a 150mm cg and its stabalised the wing rock when steering a harrier, I feel it could go back further as it didn't make any difference in its pattern abilities, the plane was still very smooth and stable on landings.
I have lost about 4 canopy retaining screws now in flight, so will drop some thread lock in the T-nuts to make a tighter fit. Also make sure the wing retaining threaded stud enters the fuss past the nut 10mm or more. (ie, don't glue it too far into the wing) You will then be able to stop the retaing nut coming loose in flight by a cable tie or pushing over some silicone fuel tube.
happy landings.