You can actually use Seasoned Salt as your primary rub... IMHO, you really don't need to inject but feel free if you want to... I think you are going to need more charcoal, so pick up a couple of extra bags, it's not like they go bad (unless they get soaked in the rain... Don't ask me how I know this)... and my guess is that you are going to smoke more meat any way so why not have it on hand? You are also going to need a cooler that can hold the butt.
Depending on the size of your butt (I'm not getting personal here), and I do recommend a 'Boston Butt' about 7 pounds, it could take up to 10 to 14 hours when cooked at the temperature I recommend, 225* (just remember one of our golden rules, "It'll be done when it's done") so buy some extra beer and cigars for the guys that are going to stop by... I would also pick up a meat thermometer that you can put in the meat and leave it there... They run maybe a buck or two and is a good start.
Now for the run down of what is going to happen...
1.) You are going to rub down the meat between 4 and 12 hours before you plan on putting it on... This really does nothing but give you something to do because you are going to be to excited... It is also at this point that you could inject it if you wanted... I like the 'KISS' theory so I don't, but again, it's up to you...
2.) Get your charcoal going (without the use of starter fluid please). I like a chimney starter. Also do a quick search on the 'Minion Method'. This should explain how you should lay out your charcoal and wood chips. Another thing, you don't need to over load with the wood chips... A little can go a long way... I would rather have a cook be a little light on the smoke than to heavy...
3.) Once you get your smoker up to temp, put on your pork with the thermometer inserted and NOT touching a bone. I like to cook it fat cap up, some insist it has to be down... Just remember, I'm right... lol...
4.) Keep the cover on the cooker... Remember, if your lookin, you ain't cookin!!! When you notice your cooker temps drooping, Start another 1/2 chimney of Kingsford (I do this because I can really smell KF when it is just starting and don't want that smell on my food. Once it's going, add it to the cooker). It is at this time you can check the temp of the meat. At some point in your cook the butt is going to get 'Stuck', normally between 160-165*. This is normal, and this is when the meat is getting real tender. This period can take a number of hours and is nothing to worry about...
5.) Once the meat gets to about 195* you want to check it... you do this by inserting a fork or steak knife and 'feeling your meat'. It should go in like 'almost soft butter' (NOT MELTED BUTTER, SOFT BUTTER!)... Now is the time to take it off and wrap it in foil, then wrap it in a towel and put it in a warmed cooler (warm it with hot water for 15-20 minutes and then dry it out). Let the butt contemplate the meaning of life there for a solid hour...
6.) Now that your pork has been enlightened, remove it from the cooler and let it rest on the counter for 25-30 minutes. This allows the juices to re-distribute and keep the meat moist.
7.) You have now completed the cooking portion of our program, simply pull the meat with either your hands (it's going to be hot!) or with a couple of forks...
8.) This is the most important rule that I'm going to give you. It's BBQ, and even with how serious we are about it, it's still only BBQ so give your self a break and have some fun!!!! Remember, we don't shut down the site on weekends or holidays so if you have a question, just ask, some one is going to be here for you...