Secure storage not reflected by postcode?

Hi, I am about to commit to storing my campervan securely within a high steel fenced and locked compound.

When I told the Caravan Club Insurance my plans they checked the postcode and told me that it will put the premium up by £35 per annum compared to my continuing to park the vehicle on my drive? 

There was me expecting the premium would be reduced.

Seems that it doesn't matter whether it's locked within an armoured steel box hanging from a crane - the postcode determines the risk regardless! 

I would be interested to hear other owners' views who have experience of this?