I tend to "explore" using Google Maps in Satellite view, that'll give you a pretty good idea of spots that could potentially allow for a van. Specially if it's only one night, you won't have much of an issue there.
Needless to say that you shouldn't even think about touching sand with a campervan unless you have an AWD converted van and even at that, with the extra weight you could be spending more than one night if you know what I mean.
