deweymeats Philly brat is meant to be a fresh product not a cured sausage. This matters because the salt content of Philly is designed for a fresh and not cured brat, salt helps solubilize the proteins in the meat, without it you are always going to struggle, your fat will render out and that can give you a dry finished product and since the casing has been dealing with more fat it can cause issues there too. Also, if you are smoking, you don’t want to use 30mm fresh collagen, use the clear as that is designed to be smoked, the fresh is designed to be grilled or cooked in the oven.
What are you doing when they come out of the smoker? Are they given an ice bath, do you leave them out for a few hours at room temp and then store overnight in a cooler?
I also don’t like Carrot Fiber as much for Cured Sausage as I do for Fresh Sausage. The Sure Gel is a better option for cured products. I don’t think this had anything to do with casing toughness but it is worth trying.
So if you are still wanting to use the Philly for a smoked brat I would use about 10% less meat to get the salt content closer to a cured brat, use collagen casings that are designed for smoking (clear probably sounds like what you’d want) and use sure gel. Hope it helps!