You could always wall it in!
I think you are allowed to erect fences without planning permission. It does sound like something you could perhaps illegaly do but i'd want at least some utilities installed, and i'm sure people would start to notice if i'm getting power lines laid.
Also I can't help myself, i've been thinking about this again. Was wondering if forest management would count as a valid reason to have a semi-permanent residence on site. From what i've read the answer is no, but I found some anecdotes about charcoal burners being given permission to live on site. And that makes sense since those kilns need to be tended.
I've also read that there's fairly relaxed limitations on the size and shape of any buildings on the land as long as they're for forestry purposes, but forestry purposes is extremely loosely defined so I think a woodworking shop could fit. Along with the hot tub and sauna. But what's more interesting is the idea that power and water might be essential, as well as bathroom facilities, and probably a phone line too. So perhaps getting that installed would be achievable (if very expensive).
Alot of UK law is fairly vague from what i've looked into. Lots of catch-alls that kinda define things more by their intent rather than their actual structure. But when it comes to caravans everything is shockingly clear and well defined. It's almost as if they want to prevent a certain group of people stalling evictions through lengthy legal battles...
As always this is
For Entertainment Purposes Only. I'm only half serious but I think it's fun to think about.