I'm using Energy Squadron SFL120 battery's too, been trouble free for 5 years so it's a shame they're no longer in existence.
Numax CXV being a fairly deep cycle, marine sealed battery with good cranking amps looks like the only economical replacement.
It would be interesting to hear from people who are running these type of batteries to see if they're any good.
BTW Stainless 304 will be fine for the nuts and be cheaper than 316. Shame you didn't live closer as I could have spared a couple of M12's Brian
Looks Slow but is Fast
Member of the ebay Blue RIB cover club.