Here is the letter that Camp Sweeney supplies for their camp.

TO WHOM IT MAY CONCERN: __________________________________ (DOB:________) has insulin dependent diabetes mellitus. Due to medical necessity he/she was referred to Southwestern Diabetic Physicians Association, Inc., in Gainesville, Texas for intense diabetes control management program designed to initiate compliance with the necessary therapeutic recommendations for improved control, thereby decreasing the potential incidence and severity of chronic, recurrent complications of the disease.
Sincerely,
_____________________________

Your doctor should copy this onto their letterhead, sign it and send it to either the camp (which Camp Sweeney asks) or to your insurance.