D.D.
My little one is in the same boat. He doesn't use it to get out of naptime, though. If we are at dinner, he will ask for the potty four or five times, usually just when my food comes. It's hard because you don't want to discourage, but you just want to eat your food! I usually take him once, then try to distract him back at the table before he thinks about asking again.
As for public restrooms, I bought a portable cover to go over them at Babies R Us for about $10. It's heavy plastic, so you can just wash it in the sink after he's done. I keep mine in a ziplock so it doesn't touch anything else in my bag. It comes in handy.