You usually need some sugar in the rub to get nice bark. Wrap in foil (if you are going too) at the latest possible temperature. The longer you can wait the better. Bad Byrons Butt Rub gives a decent bark. Basically just like a Boston Butt, just a bigger hunk of bone.
I use a basic Paprika, onion powder, garlic powder, salt and pepper rub. I coat the butt in mustard (the mustard flavor cooks off) first then apply the rub. The mustard helps to make a great bark. I also do not foil at all. It may take a little longer but just wait it out and you will have a great bark.
I use Paprika, Garlic Powder, Onion Powder, Brown Sugar, Kosher Salt and Pepper. I do not use Mustard; I use Honey to make the glue for all these spices. That made for a much better tasting Pork roast.
I did a pork roast, started out I wanted to do it my pressure cooker, but that is another story. It was no go. But to start, I put some salt, pepper and Italian Seasoning on the roast, and then browned all sides in a little olive oil. It then went in the Pressure cooker, had problems, off to oven it went. Let me tell you that was the very best pork roast I have ever had. I plan on putting together a rub using Italian seasoning this year
I rub the pork butt down with extra virgin olive oil and apply a very generous portion of my rub. Then, I inject with 3/4 parts apple juice, 1/4 part apple cider vinegar, some brown sugar, and rub. Now, I roll hot and fast 275 to 300 and smoke to IT of 165 then, I wrap using some of the same mixture I injected with. Finished when IT hits 205. Put in 5 day cooler for 1-3 hrs. My butts don't have a lot of bark but tons of great flavor. They've made me plenty of money. Rubs are to easy and cheep to make yourself. Try Equal parts dark brown sugar and paprika, some kosher salt, course black pepper, granulated garlic and onion, cumin, and cayenne to your taste. Have a good day "A''