Pulled it out. Now I've got to rid it of the mice. Cat probably wouldn't like being locked up in it. Rather not reach under the seat to find the rattlesnake.
Put poison blocks in the car and a big bowl of water near the car if possible. The mice will head for the water after eating the poison. You should find a bunch of dead mice near the water source. Of course you have to decide if poison is safe for your situation.
Put a 5 gallon bucket in the car with a piece of wood leaned against it. Place a few pieces of dog food in the bucket. The mice will climb the piece of wood and drop into the bucket to get the food. Then they can't get out.