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A bit off the OP's original query, but I keep a Montauk in the water in So Ca. and I also applied the Interlux epoxy barrier coat under the 'rolled-on' antifouling paint w/out any diminished speed noted.
But I 'barrier coated' specifically as insurance against water ingress thru the gel coat, not that you will ever stop it completely [nature always wins], but as far as I know, this is about the best you can currently do if you plan to keep a f/g hull in the water.

FWIW, Many might already know, but for benefit of others,
a few very important steps before applying epoxy barrier coat/antifouling paint:

Make repairs to gelcoat [and any laminate damage] and ensure a fair gelcoat surface.
Clean gelcoat w/prescribed wash solvent [can't remember Interluxs'].
Apply barrier coat primer asap after gel coat cleaning.
Apply barrier coat within prescribed time window after primer [temp dependent window]

All of that, depending on size of hull, can be tough to accomplish in one day by one man.

I put 2 coats of Interlux epoxy barrier before my antifouling [Interlux UltraKote in blue].
It's been 3 years this July and just in the last 6 months I have increased bottom [wiping] cleaning to every 30 days [vs every 90], and even then, I just use a piece of trailer bunk carpet[in/outdoor carpet] to get the 'bio-slime' off and an old credit card as a scraper for any hard growth that tries to start.

BTW: Except for gelcoat repairs, I collaborated and sub'd to boatyard all of the prep and coating work for best outcome and so far it's wearing very well.