Nice one (in a way, you know what I mean)...
We usually do long weekends, leaving at half 3 Thursday, a leasurely drive to the tunnel for the twenty past twelve train (its cheap then) then once on the other side drive to the services just north of Aachen (bout half three) and just sleep in the car till rush hour passes by, at the track for ten on the Friday, track Friday, Saturday, Sunday (if possible) and drive back to Calais Sunday afternoon, chill, Monday morning train and a gentle bimble up the road (the worst part of the whole trip)...
Anyone down south of England, you dont know how lucky you have it, its just so much easier from there...
It can be done for the cost of a long weekend back home, ok if you dont go lots and get a season pass the cost of laps mount up but even then no reason not to give it a go...