Sealants won’t stick to Starboard well enough to seal out
water over time. [I have Starboard on my foredeck in front of
windlass for the same reason.]
If you are concerned about it staying wet underneath, consider elevating the Starboard slightly above the teak so water can drain and not be trapped.
e.g., Use: beads of caulk that the Starboard sits on top of after caulk is set; O-ring(s) around fasteners between teak and Starboard as shims to create a gap; etc.
In case this helps.
Cheers, Bill