Hi RA,
both my original BRex and my current (10yo) BC26 were Copper-coated from new by Swallow.
The coating extends to the whole board/lift-keel (same on the BC26), and on the BRex the inside of the board trunk/box too. I have yet to see up inside the BC 26 keel trunk.
antifouling is definitely needed!
As well as in the dead-water areas of the lower trunk F & A (mussels liked the area around the hinge pin), I found several small mussels growing high-up inside the board trunk on the BREx when I removed the wood capping, attached to the coppercoat...and very much in the dark!
However, generally, I would recommended the coppercoat, and would have it again. It MOSTLY works.
That said...I have this year decided to overpaint (with Seajet Emperor 34 £130ish 5 ltrs. same paint as used on the saildrive leg) the permanently-immersed twin rudders on the BC26. They seem to "weed-up" very quickly, I generally need to give a light scrub every week. I guess this is because of the way their vertical area is exposed to well oxygenated, bright surface water?
Coppercoat saves a really horrible chore, which is particularly unpleasant and time consuming on trailered boats like mine. perhaps consider against the cost/aggro of 8-10 years of applying conventional antifoul?
Being epoxy, they say its an excellent osmosis preventative too. Perhaps worth considering osmosis prevention if the boat is spending long periods afloat? but I'm not sure that I'm entirely convinced of this aspect?
Both boats moored on the Fowey, the BRex on a semi-drying mooring over sand (possibly a bit brackish?), the BC26 permanently afloat (April to October) on a deep water mooring near the docks.
I would say that the Fowey is nowadays a heavy fouling area, made worse imho by the recent development of the mussel farm processing plant, and the invasive Pacific Oysters.
I added more coppercoat (at VAST expense!) to the internals of the BRex outboard well. That worked, but painting the well flaps was a hopeless waste of time and paint. it won't stick - not that I was surprised, but I used up my "left overs".
I beached and scrubbed both boats mid season/pre significant events.
A "scotchbrite" liven-up, as recommended by coppercoat manufacturers seems to do the trick.