I've been thinking of going on a cheap 'camping' holiday, sleeping in the back of my estate car. I mentioned this to my neighbour last week, expecting him to think me a little eccentric. Instead it turned out that he does exactly the same thing himself, all over the country. (He's a keen fan of motor sport and goes to lots of events). He told me that he always books onto camp sites, and he has never had any problems.
Chris
PS: To find suitable campsites in Wales, start here:
http://www.ukcampsite.co.uk/sites/county_adv.a sp?region=Wales
Select your county then, on the next page, define your requirements (including, of course, setting 'MotorHome Pitches' to 'Yes')