joduff have you considered inedible collagen? It takes some special preparation but it after that it does a good job on dries sausage. If you don’t want to do that I’d suggest beef middles, it’s what we used when we made a bunch of dried salami at waltons and they worked well for the most part. Just watch the strings when you truss them, dipping the strings in vinegar or something will help prevent unwanted mold, also using a “good” mold isn’t the worst idea!
Good luck and as always, take pictures!