I use Teflon tape, 2 wraps of the threads and it has never failed me with any of the substitute, and that includes the original substitute that we commonly refer to as smokeless powder. In some instances I will also lube the surface layer of tape sparingly with copper bearing anti seize commonly available at any auto parts store in small tubes. ( ask for oxygen sensor safe anti seaze ) That is to allow it to the tape, to glide in the threads easier. I have also over lapped the end of the plug slightly with tape to help it seal where it should squarly butt up against the step in the barrel to give a better seal.
I have always told people grease is your friend! I use the tape to close up the tolerance of the manufacturer that has made the barrel and the plug to both +- tolerances, not an opinion but fact. If your BP wiggles in the threads as most do when threaded in, then there is lots of room for fouling. IMHO, If the threads of the barrel are not smooth then it can rip, roll, ball, ball up your tape, so a little grease on the tape will help.
Did you notice I reffered to the copper bearing antiseize as oxygen sennsor safe, yes it is. It is designed for high heat applications. exhaust pipe applications, so if you ever have to apply heat to remove a sticky plug it will not cook out and turn in to just more carbon.
Good luck,
Ken