There are two reference books that will help:
1. The Collected Papers of Milton H. Erickson, M.D. edited by Ernest Rossi, Irvington, 1980. Check Volume IV for the section on pain.
2. An Uncommon Casebook: The Complete Clinical Work of Milton H. Erickson, M.D. edited by O'Hanlon and Hexum, Norton, 1990.
A more traditional expert who has written about hypnosis and burns/pain is Dabney Ewin, M.D. at Tulane Medical School.
Good luck with your work.