Anyone have any advice or experience trying to use these certs last minute?

I am going to be making a long drive over the summer across a large piece of the country. I want to drive as far as I can before I get too tired but don't know where that will be so I can't make a reservation in advance. Also because it will be around midnight, the strategy of making multiple reservations won't work. Would it be possible for me to show up and ask to use my cert?