Double 11 gunners are absolutely fine for UK. Wait for vet conversion rate boost event and give them 150 vets or so.
Even at 109 vets (full experts of course), they'll cap their abilities around level 90, roughly, when classed on time.
If you want smoother grinding experience, I suggest you delay their class at level 42 and wait till level 65 or 61 (when you can use PBB), then class them to Reload Huge Gunners directly.
So what gun to use between level 42 and level 60+? Use 8*2 N on County or Surrey. Yes, it's NOT a heavy gun, so it won't require Heavy Gunner. 8*2 N is beast in Blitz. It's got both range and power. Try hitting your target at 70 degree; it takes a bit of skill but you'll see why and love it.
If you ask what the best sailors for UK gunners are, I'll say Elite Repair, with late-classing and help from vet conversion boost event of course. But considering this game is dying, you probably don't need to bother with this...