Recommendations for protective finish for "Mahogony" (Red Merranti) deck?

[blueman]

I'm refinishing a covered deck with tongue & groove 1x4 Red Merranti.

Looking for recommendations for protective finish?

- What should I coat the underside (and tongue/grooves) with before installation?

- What is the best natural finish for the topside after installation?

Thanks

[beecrofter]

Look into "Penofin" not cheap but very good