I'm afraid all this should have been covered in your tenancy agreement - what was included, who had the right to which parts - including parking your own camper van, which parts you were still going to maintain (garden etc). However, it's a bit late now. I honestly don't know if the word of your witness would stand up in a court of law if it came to it. When does the current tenancy agreement expire? I'd be tempted just to cut my losses for now, and decline to renew when the current agreement runs out - and next time, get a detailed tenancy agreement drawn up.