I think the law in England and Wales means you are only allowed to stay on campsite for 28 days. After that you have to leave, I think for at least 24 hours before returning. The law in Scotland might be different. I would suggest rotating between 3 or 4 campsites in the area you need to be in, stay in each one for 4 weeks at a time, You might get a discount from the sites owners for staying for 4 weeks. Always keep looking out for deals, especially during the winter months. Some campsites also close during the winter months, so be aware of that.