Originally Posted by
MiddleAgesMan
Sikaflex or 3M 5200 work for the access rings. A high quality household (exterior) caulk would be OK but don't use silicone.
The gudgeons you bought for the rudder box will work but the after-most screw holes appear to be too far back to catch wood. You should probably cut the excess off and drill holes so you have two fasteners; one would not be adequate IMO. And, yes, fit spacers so that the gudgeon fits snugly.
My u-bolt is just above the air box. You will want access to it many years down the road and you wouldn't want to tear off the box lid.