Best thing you can do is to get synthetic underwear. There are many brands out there, and almost all of them work very well. They will draw the moisture away from your skin to prevent getting a rash. Next, get some airflow around your bottom. For this, the Bead Rider seat pad is king. If it is not uncomfortable for you, it is tough to beat. A million cab drivers can't all be wrong. Finally, if you still have a problem, one of the anti-rash powders such as Gold Bond or Anti-Monkey Butt work well.