I use the 12" tube for cold smoking salmon and trout.
After the brining/pellicle formation process (2-3 days) I place the fillets on racks, and ignite the tube smoker. No heat from the FEC100 is needed. If the outdoor ambient temp if over 80, I place a hotel pan of ice below the fish.
The end result is always fabulous. Trout takes about 2.5 hrs...salmon about 5.