I used to fly my microlight out of a farmers field and kept it in an agricultural shed, his old tractor was in the corner!!
I had to keep records in my flight log book by law, but it was useful as later I could demonstrate that the field had established use.
Unless it's changed, after 4 years of use, it becomes established use and the planning struggle against that.
Everything was very discrete, sheds painted green, caravan green, workshop green, actually, unless you knew it was there, you'd never find it, shown to be true as visiting pilots sometimes struggled to find it from the air.
NB, some councils are using satellite information to discover buildings built without permission, one included a shed in the middle of a woods, used as a weekend retreat and ordered it to be taken down.
If you invest in surplus camo nets to hide the vehicle, neighbours happy because they can't see it, if you go over the top then satellites can't see it AND it'll keep the sun off. If it took years to find Bin Laden, how long before you're found??
Take photo's that are dated say with newspapers, to show how long you've been there.
With a little planning, no one will ever know you are there, after 4 yrs it's not an issue.
Also, I believe that farmers can have one caravan on their land anyway. Couple of sheep and away you go, but the horse way is probably the best, they pay you.