the difference between the 3 grades relates to the security measures the facility has. Some insurance companies now insist on storing ina CAssoa compund rather than a farmers barn/field.
It won't make any difference to the premium, mine is still based on my home address (very expensive), when it's stored in a nice safe rural location, protected by 6 foot dykes on 3 sides.
Make sure you tell the insurance company where it's stored and follow up in writing, as the dear NFU did not make a note of where my van has been stored for the 3 years, so heaven knows what would have happened if I had made a claim. I ma now with the CC, who didn't even ask.
Re questions, 1) any been stolen 2) who has access and at what times of the day/night 3) security lighting 4 patrols 5) the usual suspects when looking at any new environment for very very expensicve possessions.
Hope it helps