Just found this on another site:
Ok, here goes - Smoked Backstrap:
You will need:
1 backstrap
Celery
Garlic cloves
Italian dressing
Worchestershire Sauce
Onion
Garlic powder
Mrs Dash Original seasonings
Dale's Marinade
Morton's Nature Seasonings
A smoker
Mesquite chips or sticks
Charcoal
Water pan for smoker
cut the backstrap in half, or you can do it whole. Trim all of the 'silverskin' (membrane) and fat off of it. Then, cut a few slits (about 1-2" deep, and the same length) in the backstrap. Space them fairly evenly, about 4-5" apart, and staggered. You don't need but one every 5" of backstrap length. You'll use this later. Coat (not too much, though) the backstrap in garlic powder and Mrs. Dash original seasoing. Let this sit for about 30 min to an hour.
Now is a good time to get that charcoal going, and put the water in the smoker pan. It's best to soak the mesquite chips in water overnight, so that they burn longer, and release the smoke over a longer period of time.
Next, Coat the meat in a good sprinkling of Morton's Nature seasonings. As finely as possible, chop celery, onions and garlic. Mix the onions, celery and garlic and insert it into the slits you cut earlier. Liberally sprinkle Garlic powder (again), Mrs. Dash, and Morton's Nature Seasonings over the backstrap.
Take another onion, and the leftovers from the 1st one, and cut into slices.
Crush 2 garlic cloves, and cut up the remaining celery.
add this to the water pan of the smoker (should be almost boiling now. Also add the worchestershire (about 1/4 cup, 1/2 cup of Dale's, a liberal amount of Morton's, Italian dressing, Mrs. dash, etc. to the water.
Place the backstrap on the grill, and put a little italian dressing on top of it.
Smoke for 4-6 hours, keeping an eye on charcoal, and water, adding when needed. Keep in mind that most of the flavor comes from the water pan. Cut into the backstrap at 4-6 hrs, to see if it is done. Leave on longer if needed. In a pinch, you can wrap it in foil and put it in the oven for the last 30 min. or so, if weather conditions aren't ideal (ie, too cold, windy, etc.)
It is a little trouble, and it takes time, but the backstrap will have a wonderful flavor, and will melt in your mouth!