I once came up with the idea of having a secure instrument creche for festivals - a secure van with a security guard where, for a fee, people could leave their instruments and then retrieve and return them at any time of the day or night. Might be a project for my retirement.... if someone doesn't do it first! How much would you be prepared to pay for that facility? Make it worth my while and I might retire early!!!

At the moment I leave them in the car - they're covered by insurance as long as they aren't visible. Not ideal but the only solution so far.