There's a man close to me who has caravan storage, very secure, but obviously on the side of the road. He used to charge £5 a week, that was about 5 years ago so it may be more now. I see a lot of caravan storage on farms I go to. They are often hidden from view from the road, I only see them when I get round the corner, but just because they are hidden doesn't mean on-one knows they are there.....Google earth makes anything like that insecure, some of the security on those places is better than others.
I presume you are looking for somewhere to park your motor home? I can ask if no-one comes up with a better answer. When you talk about it, it sounds like you will need a good secure place for it