My dad has been cold smoking chum for decades and everyone likes it.
1. Split the chum (like filleting but cut from the dorsal side and leave the belly intact to hold the two sides together).
2. Put the fish in a simple brine - layer of fish, generous sprinkle of rock salt, layer of fish, layer of salt, etc.
3. Go cut down an alder tree and split it. This takes a few hours, during which time the brine is doing its thing.
4. Hang the fish on split cedar sticks in the smokehouse (tall lean-to, like an outhouse, built from 2x4s and plywood, with a burlap flap for a "door") by threading the stick through a few times near the head end.
5. Light the fire and keep it small and smoky (obviously). The green alder gives off really nice smoke.
6. Stoke every few hours for 3 days or so.
I know it's pretty old school and I don't know how you would adapt it for a commercial smoker. But that's the way he does it and everybody raves about the fish.