Eventually we will reach the point where I will have him in underwear and pants in the car. I know there will be accidents, which is fine, and will bring a change or two of clothes. But what if he pees IN the car seat? A towel is safe underneath him, right? I don't want to make it unsafe but I don't want him to sit on a soaking wet cover either, there is no where we'd go that even on a hot day would be long enough to totally dry it out. Or do they sell spare covers I could buy?