I was able to torque down the nuts tonight, but not sure how far I can go. The walls of the cb trunk have not started to squeeze in yet, nor has the fg started to crack. I do believe I am compressing the washers more, but the nut certainly has not 'seated' yet. Inspection from underneath, with lights shining on the nuts from inside the bilge does not appear to show any light ie. no visible cracks or gaps.
I think at this stage, I will apply some heavy white lithuim grease to each side of the nuts, and drop it into the water and see if it lets water in or not.
Any experienced comments at this time would be welcome!