On our B30 the harness eyes were fitted on the front and sides of the binnacle, the front one being reachable from the companion way, these can be fitted through the binnacle access panels in the aft cabin. We also had eyes fitted on the side decks and foredeck for the jackstays. The eyes on the foredeck were aft of the hatch and from memory slightly wider apart than the hatch is wide, we had white rubber bungs covering the holes in the forecabin needed to access the nuts and can only suggest that how ever much stickaflex you think you need to make the eyes watertight, double it. They are a real pain when they leak as it runs down inside the inner lining and takes an age before you realise they are leaking by which point the rear of the linings is ruined. The rear eyes were easy to fit as one was located over the cockpit locker, the other was behind the shelf lining in the aft cabin, again I recommend lots of sealant.
If you have teak decks you need to ensure the area under the padeye is well sealed to stop any chance of water getting to the plywood backing and rotting it away. One solution you may want to consider to avoid any problems is to drill the toerail and fit shackles for the jackstays rather than drill the deck.