Has your potty-training child ever had an accident while in the car?  We've been there, and then I discovered a way to make it a little less risky to put your child into the carseat, without resorting to a Pull-Up.  There is a product called a Piddle Pad that can be placed into the carseat to essentially collect the liquid, so the carseat stays dry.  You can then remove the pad and put your child back in.  These pads are relatively expensive, and I found a cheaper alternative.  A "lap pad," sold in the baby section with bedding and such, is a thin and absorbant pad that is about the same size as a Piddle Pad and does the job just as well.  I keep one in each carseat and several extras in the car to replace if one gets wet.  They fold up very small, so they don't take up too much room.  Keep some plastic bags in the car to store wet clothing and pads, and you're good to go without the stress of a wet carseat.