You are doing it wrong. You need to take some advice from a seasoned Aire, Stelplatz and wild camping guru and general motorhome Yobbo.
What you need to do is two things. First you seek out a corner or end pitch. That way nobody can park on one side of you at least and even, YES EVEN if there is several acres of space and no vans some fecker (and Brits do this to) will come along and park next to you so think ahead!
Secondly you need to become the Aire yobbo. Spread out! Claim your land! Who won ****** anyway I say! (Try not to mention the war, I did once but I think I got away with it). Buy a guitar even if you cant play it and leave it next to the van with a few scattered empty super strength tramp lager cans strewn about, packet of fags etc. Maybe think about erecting a washing line and hang out a few T shirts with "Death to all motorhomers" or Summat written on them.
Here is a good example. Look how the yobbo has occupied an end pitch on an aire in the south of France. There is no chance of anyone coming within a hundred yards of this idiot.