Campervan

Your son would do well to contact CAMC direct and ask the question. They do have rules about which vans can be used on site.

Can’t see why the club would have a problem. See van conversions on CLs 

CAMC have certain rules about what furniture/equipment is permanently fitted.

This might help the OP.

Outfit Rules

We came across an interesting first last week at Burrs Country Park. The Club Site I believe is a “no tent” site, but there was a very nice roof mounted Tent box, with awning, on one pitch. Had a hook up I think as well. Pitched close to loos/showers, owners young and lithe enough to cope with the ladder🤣 very nice touring option.

I hadn’t seen the link you posted WN, but it’s good to see that the Club has become a good bit more open minded around touring outfits. Safety is of course in the interests of everyone. I think our Neice’s tiny conversion might be allowed now, it wouldn’t have been a few years ago.

Does a Club warden really come inside a van to check whether the cooker is “rigidly attached to the internal structure” as per the rules?
Most youngsters with a VW would simply go off to festival where the regulations are less picky. Or take their surfboards to the beach. 
Would youngsters really enjoy a Club site?

Actually the fixed cooker is part of the Motorhome definition. The club rules go on to modify that with references to self builds. Seems need to be a roadworthy vehicle, clearly intended for leisure holiday. Op says the one in question has water and beds but not a fixed cooker. There are plenty of perfectly good self builds with out fixed cooker, so that cooker can be used inside or out. Also if roof tents are allowed then would have thought the one referred in OP has more facilities.

From what I've seen on club sites recently  the days of the club being particularly bothered what type of vehicle you turn up in are long gone.   

I guess that providing they respect the rules and other people, that is all that matters.

I suspect that philosophy is behind them now being called "camp sites".....