If brining in a cooler, add ice in a ziplock bag if temperature gets over 40F.
This keeps the ice from diluting the brine.
I force a bowl or pot down on top of the turkey as it brines to keep it submerged.
Stir the brine and turkey every 12 hours or so. The salt may not disolve at first, and the stirring should keep the brine near saturation as the bird is treated.
Remove turkey from brine after about 48 hours.
Place in cold water bath for about 30 minutes to an hour.
Smoke turkey for 2-3 hours at 225F.
While turkey is smoking, remove duck from brine for a 30 minute to 1 hour rest in cold water. Allow to cure for the next hour or two in the fridge while turkey is smoking.
Place duck on top rack, over turkey. Fat will drip from the duck and baste the turkey. Make sure that the turkey breasts are in a position where they will receive the bulk of the duck drippings.
Smoke for an additional 2-3 hours until both duck and turkey breasts reach 165F.
Allow Duck and turkey to rest for about an hour, breast side down, or on the bottom, covered with foil or similar to keep them from cooling too fast.
Increase/decrease the brine as the birds vary from the "medium" size listed above.
I reserve about 1/5 of the brine salt/sugar to add along with the duck.
You can spice the brine, but it is not absolutely necessary.