I like to add a tablespoon or two of broth in the bottom of the crock pot. I think it keeps the turkey moist but who knows. Pour it into the crock pot first.
Then, combine all of the seasonings in a small bowl, whisking together. Press the spices into the turkey tenderloin, being sure to coat all the sides. Place the turkey at the bottom of the crock pot.
In a bowl, stir together the sauce ingredients: brown sugar, BBQ sauce and honey mustard. Then, pour the sauce on top of the turkey tenderloin. If using a meat thermometer, this is the time to place it into the largest area of the tenderloin.
Place the lid on the crock pot and cook on low for 1 hour 45 minutes to 2 hours, until the turkey reaches an internal temperature of 165 degrees. It will take about 8.5 to 10 minutes per ounce.
Once the turkey tenderloin is fully cooked, remove from the crock pot and let sit for 10 minutes. Then, cut the turkey tenderloin into 6 equal slices, 2 slices per serving.