I'm thinking of camping at Rincon, there is gonna be a truck and trailer and a small car. Is there an over flow or somewhere to park for 2nd car?

Everything must fit in your campsite .. There is no "overflow" area ..

Yeah it all depends on how big your truck and trailer are.. they have a bike lane that you can't go over or into..if you don't have slideouts you might have room for your car..

There is no overflow area, there is space for 1 RV or cam-trailer & 1 car