There seems to be a special powder for your problem:
http://www.socialphobiaworld.com/butt-sweat-11462/page-2/
"Anti Monkey Butt Powder is specially formulated to absorb excess sweat and reduce frictional skin irritation. It is Ideal for butt busting activities such as truck driving, motorcycling, bicycling, horse back riding, and extreme sports. May also be applied inside footwear, under sports pads, and other areas prone to chafing. Indoors or outdoors, work or play, or on occasions when you sit on your butt all day, don’t let your buns get red, use Anti Monkey Butt Powder instead!"
Relieve the friction of monkey butt and painful butt rash, when you ride, sweat and sit. | Anti Monkey Butt Powder
http://www.socialphobiaworld.com/butt-sweat-11462/page-2/
"Anti Monkey Butt Powder is specially formulated to absorb excess sweat and reduce frictional skin irritation. It is Ideal for butt busting activities such as truck driving, motorcycling, bicycling, horse back riding, and extreme sports. May also be applied inside footwear, under sports pads, and other areas prone to chafing. Indoors or outdoors, work or play, or on occasions when you sit on your butt all day, don’t let your buns get red, use Anti Monkey Butt Powder instead!"
Relieve the friction of monkey butt and painful butt rash, when you ride, sweat and sit. | Anti Monkey Butt Powder