Morning,
... in case of flush superstructure get yourself some petroleum jelly and some silicone (the bathroom/tile type) and make a watertight seal.
You will need something to clamp down the superstructure in place though, be it by screws, Dzus fasteners or any other means.
- Remove superstructure to access the support of the removable deck area.
- Make sure the superstructure support is solidly attached to the fixed deck (there will be some extended pressure).
- Put a generous and uninterrupted(!) bead of silicone on the deck support.
- Treat underside of superstructure with a light layer of petroleum jelly in every place where it will touch the silicone. Don't forget the sides of the flush deck area.
- With jelly side down put superstructure in place and fix it in place with flush deck.
- Let silicone cure
After the silicone has cured, remove the superstructure. Due to the petroleum jelly it should not have stuck to the silicone bead.
The silicone should now form an uninterrupted and slightly compressible seal on the superstructure support area.
Any excess silicone can be cut off with a sharp knife.
When the superstructure is in place it will be pressed against the silicone bead, thus forming a watertight seal.