A total misnomer.the term Marine epoxy gets used all the time,any two part epoxy will work for brushes,makes me crazy/er.
That being said,Marine epoxy is an epoxy that will cure under water,normally we never set knots under water,it has nothing to do with water resistance whatsoever.
Another pet peeve of Mine,people always say,let the epoxy Dry well before use,EPOXY DO"S NOT DRY.
Epoxy cures and hardens,Mini rant over,carry on.