To the OP, why not just stay over nearer to the port and get an early start the next day?
We just stayed over at the Ibis near the channel tunnel for a couple of nights, came to E70 for 2 adults + 1 child each night when pre-booked via the internet, standard room rate with no prebooking was nearly double that. The Tunnel hotels are quite secure too, as they are all grouped near Cite Europe shopping centre and have a 6 foot fence with security gates around them.
Accomodation wise, I'd go for Ibis over come of the other chain hotels, they tend to be a bit comfier. Campanile tend to be a bit more scruffy and noiser due to the motel style.
My Visa debit card also worked in automated pumps on that last trip, so access to fuel should be a bit easier than it used to be.