Hickory salt for smoked fish brine?

Brief question: anyone use this before? Longer context: Local guy near my family cabin on Georgian bay smokes and sells local fish - mostly rainbow trout and regular trout, in addition to whitefish. He's got a great setup, with a shed converted to a small store complete with kegerator. He keeps a freezer outside for people to take fish from at odd hours; just asks that you drop money into his mail slot. We've been buying fish from him for years. Since buying my egg last year, I've been trying to smoke my own fish, and asked for a few tips. I sure got a demo! His "smoker" is a tin lined outhouse that he converted himself. Presumably not on the original site! Fire is mostly cherry, but he uses oak as well. He tossed on some corn husks as it added extra smoke in his opinion. His brine includes salt, molasses, maple syrup and brown sugar. Key ingredient is hickory salt though, and he generously gave me a bag. Like any old timer, measurements weren't his thing. So curious if anyone knows ratios, or how much to use, for a fish brine?