Gary,
Tarakihi doesn't have a slot in this locker or your wooden retaining "bar" (I like the idea). What hull number is your boat? The slot looks a bit of an issue to me - water could get into the open space below perhaps thus a watertight inspection hole might be better. Don't know what effect this would have on strength of bulkhead and hence the superstructure, probably not much but I'm no expert on these things. However, I did fit a similar hatch to the double-skinned transom of my previous (albeit larger)boat to enable me to tighten the rudder pintil fittings - it didn't seem to make any difference to the integrity.
Regards
Chris Cobb
235/48 "Tarakihi"