I also use Google earth to look at the campsites, this ensures that I don't overshoot the entrance it and I have a landmark when I'm approaching.....

Poptop, we've done that as well, a badly signed campsite with a painted arrow saying 'campsite 200 yards' - we thought it meant entrance 200 yards further up the road, but it meant 200 yards up an unmade track by the arrow. We took the next road along to find a narrrow steep road with a T junction a few yards up with with an impossible uphill right turn or acute angled left turn downhill. We were totally stuck. Gravelly road so wheels were spinning, had to roll back down the road and out into the road we'd come from, stop the traffic with the Puck across the road, almost got it stuck in the hedge, unhitch, turn the Puck round, reverse the car into the road, rehitch etc. That time we were towing with our big estate car, not the Mini, even that couldn't manage it. In fact the Mini might have done better, at least the overall length of the two together was nowhere near the length of the estate car and the Puck so the turn wouldn't have been quite as tight. Like you I now find them on google streetmap so I can see where the entrance is beforehand.