Just an idea, but a friend of ours used a site that allowed them to leave the van for about £2/day, as it was left on a pitch ready for next time. Might be worth exploring if any sites allow that near you? So you could do it when you know you are going for a few weeks on the run? £2 a day when you weight up the fuel cost of a return trip is pretty good i thought. It was a new site that was just getting off the ground, so that might change when they get up and running to normal capacity, but they used to go every weekend.