Ever boat has those little items that are not "good" but are not bad enough to warrant the time and effort to overhaul them. The aft deck lockers on the Whitby 42 fall into this category, IMHO. They are excellent storage lockers but the lid is a simple fiberglass molding that fits into groves on the deck. A gasket is inserted here to keep the water out. As everything is flush with the deck this seldom works. The lockers have drain holes on the transom to let water out but the lockers tend to get wet and grubby.
Some time go I bought two;
Innovative Product Solutions M-1330-AW / 520-503 13 x 30 Arctic White Boat Deck Hatch
These were the closest fit that I could find. They are big enough for the fiberglass LPG bottles that I plan to use.
They will be mounted on 1/2" starboard to get them above deck level, but have their own seals and locking mechanism. This is what the dry fit looks like;