Tj,
As John has mentioned, just repeating your version is not going to achieve anything. Ideally the other owner will admit liability and pay for the repairs, however as he has obviously not volunteered to do that then you have the very difficult job of trying to prove his negligence. Without a witness who can state he actually saw the damage being caused, I am afraid you haven't a leg to stand on and will either need to pay the repairs yourself, or claim on your insurance. You have no claim against the owners of the site but of course, you can move your van to another site if you wish. You are in the same position as someone who has their van on their drive at home, and it is damaged while they are either at the back of the house, or out. Unless you have actual legal evidence, then sorry, it is a tough world.
To try an answer John's other points regarding CASSOA sites as someone who has used one for the last 5 years, with I may add, no problems whatsoever.
It is impractical to have a site employee to move vans in and out as many owners wish to arrive and depart outside opening hours, especially in the winter months when it is uneconomic to have someone available all day. In my site, if you wish to arrive/depart outside working hours, a key is given on submission of your site identity card and if it is not returned you are charged for the replacement, and do not get that concession outside hours again. Also as the site I am on has over 350 vans it would be congested in the summer months at weekends when sometimes 10 or more owners are moving in and out at the same time. To achieve that objective would mean a significant increase in site fees in terms of labour costs and equipment. I cannot see people sitting waiting for up to an hour just to get their van. Just think of the time it would take to go to your spot, lift the legs, hitch the van and then drive it back to the front gate. Then multiply that many times, and you are back of the queue??
Photographing a van every time you entered the site would be again impractical. Someone could be sitting clicking away all day at peak times. I suspect most owners would eventually decide it was just too much hassle. The downside would be many sites would close. John may feel that is no bad thing if in his opinion they are not doing what he feels is correct, but then the facility would likely be withdrawn from the market, and many owners are already finding problems with getting a place in the first instance.
Damage on sites can happen, and not just CASSOA sites. Even the local farmyard, or as mentioned your own driveway may not mean the van is immune to passing scratches. But the very fact that vans in storage sites are usually only going in, or out and are static the majority of the time usually means the chances of damage are very much lower.
At the end of the day where you store your van is your choice, unless like me you have no alternative but to use a storage site.