Prepare your smoker to 250 degrees Fahrenheit. Or, if you're using a grill, prepare it for indirect cooking. 

Rinse the raw shrimp in cold water, then pat them dry with a paper towel.

Place shrimp into a disposable aluminum pan or cast-iron skillet in a single layer. 

Prepare the spice rub. In a small bowl, add lemon pepper, celery seeds, garlic powder, smoked paprika and salt. Stir to combine. 

Sprinkle the seasoning over the shrimp. Toss to coat the shrimp on all sides.

Add the butter to the pan and stir to coat. 

Add the pan directly to the smoker grates. Close the lid and cook for 10 minutes. 

Using a tong, carefully flip the shrimp. Smoke for an additional 10 minutes with the lid closed. 

Remove the shrimp when the internal temperature has reached 145 degrees Fahrenheit with an instant read thermometer. Add 3-5 minutes of cook time if the shrimp have not reached this temperature after the initial 20-minute cook time, then check the temperature again. The size of the shrimp you use may impact cook time.

Once the shrimp has reached 145 degrees Fahrenheit, remove from the smoker. 

Add the fresh lemon juice and stir to combine. 

Serve warm or at room temperature.