You will have to prepare the meat the day before you cook it. Allow at least 8 hours to marinate and 4 hours to cook for a 5 lb. roast (bigger = longer, 45 minutes per pound on average)

The most important things are seasoning and juiciness as pork is, by nature, a dry meat. Pork is dry because the meat itself has little or no fat in it, it's mostly just surrounded by fat.

Prepare the Seasoning:

You will need a meat injector and the following ingredients:

1/4 cup melted butter or margarine
1/4 cup olive oil
1 tbs. garlic juice (your choice)
1/2 tsp. granulated garlic (not powder)
pinch of black pepper
pinch of cayenne pepper
3 tsp. brown sugar
1 tsp. Old Bay seasoning
Prepared Mustard (the yellow stuff in a jar)

Prepare the meat:

Trim the roast leaving just a little fat on it. 

Mix all the ingredients above except the Mustard. Bring mixture to a boil then let cool stirring every few minutes to release the seasonings. Draw mixture into an injector and inject the roast putting the needle as close to the center of each muscle as you can (doesn't have to be perfect). Rub the outside of the roast with mustard then sprinkle a little Old Bay seasoning all over it. Put the roast in a zipper lock bag or in a covered bowl. Put it in the fridge overnight (at least 8 hours).

Light the pit and get a nice hot fire going. Add a bunch of soaked hardwood chips to the fire. Put the roast right over the fire. Let the roast get dark brown all over. Take it off the fire and put it in a covered pan. Use a disposable aluminum pan if you're going to finish it on the pit. Note: You have a choice here, you can finish it on the pit, or, in the oven. What's nice about this is that you can take care of the browning, remove it, and continue to barbecue other things.

In the oven, set the roast in a pan and broil it until the browning completes.

Now, here's the juiciness trick. Add about 3/4 cup of water to the pan, or, keep enough water in the pan to cover the bottom. Cover it well with aluminum foil and, on the pit, set it off to the side away from the fire. Note: The heat should be at least 275ºF in this section of the pit. Check the water content every half hour and flip the roast each time. In the oven set the temp to 275ºF and do the same. 

When is it done? Use a meat thermometer and test the thickest part of the roast, 160ºF is where you want it. Here's where you have a choice. You can take it out and slice it now, or, continue to let it cook. If you continue to let it cook the muscle sections will begin to pull away from each other, and become more and more stringy. It is more apt to be dry so you must baste it from here on out. If it gets too dry you won't get the moisture back in the meat immediately, you'll only have dry meat in a sauce. I like to let it just begin to separate and I call it done, that way you have a little stringy meat and some nice slices to work with. 

As you slice it dredge it in the liquid, or just leave it in the liquid. Taste the liquid to see if it needs any seasoning.

After the first few taste testers visit be careful with the knife so you don't wind up with additional finger food.

 

Enjoy...