Hi if you find somewhere local please let me know, as we live on Burncross rd. When we got our van 4 years ago we looked around but no joy. We went to the farm you can see near J35 that store vans but full.
We ended up using Romley storeage at Slayer Lane,Baralbourgh, just off J30. We have 24hr access, area to wash caravan, electric fences, cctv all round site, also field with hook ups.
We pay £400 per year.
Good luck.