I'm not sure how this would work - I know the unmanned booths have a high barrier, and a single payment system - but does this depend on the height of your car? Caravans are charged at Class 2, but lorries are a different classification, so you might find yourself being 'telepeaged' for more in tolls because the 'sensor' thinks you're outfit is a lorry.
I've just checked tolls from Calais to Senlis and for car and caravan it would be 25.60 euros, where a 'camion' under 3.5T would be 38.00 euros - so quite a significant difference - and over a longer journey could be much more.