Make sure you include your web page's address in the MBU calendar. Speak at Roundtables and other Scout leader meetings. Write an article for the council and district newsletters. Depending on the size of your event, this may include more than one district or even more than one council. Make personal contacts with Scouters you know.
Promotion is like an avalanche.
It should start of slow and build to a dramatic end. You should complete your planning and start your promotions about six months before the event. Your first written and verbal contacts should be just mentions. If they want to know more, they'll ask. Each month, add a little more information then make the big push about three months out.