My 12 year old daughter has SWCAH and was diagnosed at birth.  She is a severe salt waster.  She, like your son, is very athletic ... travel soccer, travel basketball, AAU basketball ... She takes hydrocortisone 3x a day 7.5 mg AM, 5 mg afternoon, and 10 mg PM.  She takes .1mg of florinef in the AM.  When playing sports, she is typically fine on her regular doses, except for when it is very hot and she’s playing in a socccer tournament.  This can involve 2 or 3 games in one day in 80 + degrees heat.   Under these circumstances I do give her extra hydrocortisone and salt tablets and Powerade (like Gatorade) to drink.  It makes all the difference!.  My endo concurs.  Good Luck.

Michele