I am not so sure about the 'poor downtrodden bit' If the news today is anything to go by where another field has been 'hijacked' over the Bank Holiday weekend and 50 lorries and heavy moving equipment were on hand to change a peaceful village meadow into a fully set up, and totally illegal, campsite, then there is plenty of money in the travelling fraternity.
Before long they will be the ones hiring you the pitch.
However, to get back to the OP, I do not feel that most sites would be too concerned if they see a normal touring caravan with a family on board, even with a van at thefront. Just as long as you do not open it up to reveal a complete trade outfit inside. An explanation along the lines of 'I borrowed it for the weekend' would probably suffice.