I think that carrying a gun is a bad idea and likely to get you in way worse situations than you are currently facing. From your post, I am guessing that you are pretty attractive. guys driving down country roads usually drive pretty fast right? How about giving some thought to changing how you look? Not uglify, but just throw them off. I know a woman who always rides with a backpack on because it interferes with the ability to determine what her gender is by an observer. Maybe put your hair up? Lastly, carry a cell phone and take it out if someone stops you ( I agree with Litespeed that you should not stop if possible). If they see that you have a cell phone and can call for help they may not try anything. Also, if someone stops you and makes an obscene comment, call the police right then and there. That should get rid of them.
Hope this helps. You should be able to ride our bike without fear or harrassment.