Mix the salt and water into a large pan to create a brine, using heat to dissolve the salt.
Transfer the brine into a bucket large enough to accommodate the mackerel.
Once the brine has cooled to room temperature, completely immerse the fish into brine for 90 minutes.
Use a plate to keep the fish beneath the brine level.
Use fresh water to rinse the fish clean of brine and hang it out to dry overnight in a cool and dry area.
You might consider threading a hook through the eyes and hanging the fish from it.
As for storage spots, you may be able to rely on the food chamber of your smoker, depending on the local temperature, but you can always resort to the fridge.
Cold smoke the fish at 100°F for 4 hours, immediately followed by 2 to 3 hours of hot smoking at 200°F.
The fish will be done when it takes on a golden brown color and reduces to 75% of its original weight.
Carve the fish up into pieces and serve on skewers.