Balau Initial Treatment

[Guidogidday]

Over the years, the marine ply roof (800x800) that sits on the deck and tucks in underneath the window has perished. Feeling zealous and want to dress it up with some balau slats. Plan is to replace roof with 9mm marine ply, seal it and then glue/screw slats (6mm) on top. Have been told that slats like to breath so not sure whether to seal it with 2 pack and then oil it or just oil it? Should I also leave a bead of sikaflex in-between slats? Any advice would be much appreciated as I hope to do this right the first time!
Cheers.