I've tried both the "trim the fat" and the "untrimmed". IMO, either works, and they both tasted good. The untrimmed version, when you pull it off, you'll have a lot of the fat cap come right off since it'll be stuck to the grill.
As far as rubs, I've never tried Chris Lilly's, but I've heard a lot about it, and what I use isn't that far off from his.
Mine has sugar,brown sugar,kosher salt,paprika, crushed red pepper, cayenne, garlic, onion,cumin,lemon pepper, black pepper, chili powder, honey powder (when I have it), molasses bacon seasoning (made by McCormick...look for it), ground mustard,and a couple others.
I've also done the "slather it with mustard" and not. Again, both ways are fine. Having the mustard on it, I think helps retain some of the moisture and keeps the rub in place. The last one I did where I coated it in mustard, just seemed juicier.
Either way you do, make sure to put a nice even thick coat of rub on it. Fire up the OKJoe, and throw that bad boy in the middle of your smoker. Use cherry,hickory,or apple wood to give lots of smoke. After about 4-5 hours, take it off, and wrap it. I put a stick of butter all over mine, spritz some apple juice all over it,a little bit of worcestershire sauce, and sprinkle a little bit more rub on it. Wrap tightly and throw back on the grill for about 2-4 more hours. Check your temps, and once the internal temp hits 195, take it off and let it rest. Then, pull the bone right out, and start pullin'/shreddin' and enjoyin'.