Wood countertops?
I know exactly what your goin for, have done a couple of bar tops like that, but not for something your going to be prepping and cutting on, HD would also probably frown on that, just my 2 cents.
Helmsman is good. It's what I used.
Spar varnish has some flexibility to accommodate the temp changes and flexing of spars without cracking.
My cooker counter has been out in the weather since february and looks new.