I've been welding SS in a marine environment for a "few years".

Tri-mix can be a problem for the "hobby welder" because it's generally not available in smaller size bottles. That combined with the cost. I don't use that much, but I keep a 330 on hand for when I do need it. I've cut out/replaced too many SS welds that were done with other mixes to cut corners.

When it comes to Ed Craig, I'd take what he posts with a grain of salt. I think, more than anything else, his propensity to go against "industry standards" is more to sell books/advice than it is to help the welding community. Much of his advice, based on my own personal experience, is flat out wrong.

I personally cannot recommend an alternative mix/blend (covering gas) for SS, because I haven't used them myself. With the cost of the base material (SS), and the pre/post work involved with it, I just can't see cutting corners on gas.

I sure wouldn't recommend anything else for an underwater application in salt water.

With that said, I wouldn't be using mig to repair a cast SS shackle in the first place.