Regarding the tying of Costco's Boston Butts: Jim Minion, one of our great members who knows his way around grills and smokers told me a few years ago that he doesn't tie boneless butts - he just seasons them and smokes them open so there is more surface area for seasoning and smoke. I tie mine to conserve space in my 18" WSM, since I do 4 of Costco's butts at a time, sometimes 6 depending on size. If you are tying, be careful about seasoning the interior so that you don't wind up with pockets of seasoning that don't blend into the meat during.
Sometimes it takes more twine than other times. One time, I swear I used half a pound of twine because so many pieces kept escaping the ties. The meat, though, smokes up very well and very tasty and juicy.
Rita