Short-term Storage

We are soon to embark on what we hope will be a near all year round caravan touring venture in the UK. There will be a few occasions when we would be looking to return to our 'home' area for either a few days at a time or maybe up to a fortnight at most. However, I cannot seem to find any suitable secure storage sites that are willing to accommodate us. Those I have inquired with so  far simply tell me that I would either have to pay a full 12 months storage fee (or 6 months at least). In my case that is simply a non-starter as i would probably only be using the facility for a few weeks each year. Are there no secure sites that take short-term storage bookings?  I find this rather surprising, particularly outside of winter months, as many of these sites would surely have plenty of unoccupied spaces that they could earn extra income from if they accepted the odd days or weeks from people such as ourselves.  Can anybody help us with this please (I'm particularly interested in finding a suitable place in the North Lincolnshire/North Nottinghamshire area)?