The best advise is probably to keep the diaper area especially clean. Then, try to keep it as dry as possible. A rash indicates the presence of bacteria, and they need heat and moisture in order to thrive. You can't eliminate the heat, but you may be able to improve the moisture problem. Also, the longer you stay in a diaper, wet or dry, the more opportunity the bacteria have to multiply. With a rash, you likely should change every 6-8 hours at the most. I believe if you wear a diaper that is extra absorbent that your rash will clear up. You may consider using a barrier ointment, or simply extra light olive oil to protect your skin. If you use cloth and protective pants, any oils will attack the protective pants. With disposables, the oils aren't usually in contact with the diaper long enough to be a problem. Since you are already subject to a rash, use of an external catheter may cause you similar problems. Consider sleeping on a (cloth) bed pad instead of in a diaper and plastic pants, too.