Listed below are a few recommended adult summer band camp experiences.  If you know of others you could highly recommend,   submit  recommendations and feedback here.

Interlochen Symphonic Band Camp
Interlochen, Michigan
Focuses on Precision & Performance
Concert Band, Chamber groups

Snow Pond New England Adult Music Camp
Sidney, Maine
Focuses on  camaraderie and providing opportunities to try new things.
"Your best is always good enough!"
Three levels  challenge:  Advanced, Intermediate, and Beginner

Band Camp for Adult Musicians
Huntingdon, Pennsylvania
Focuses on lots of sight reading
Strong intermediate and advanced players
Concert Band and Chamber Groups