Holy smokes Carol. You didn't mention anything about security when you made your first post. LOL. That is a problem. Can you you latch the roof down and double lock the building? If not, perhaps you should dismantle the expensive stuff when leaving.
There is a bright spot however. Your personal belongings are insured under your homeowners insurance policy. You should make an inventory and speak with your insurance agent to see if they will cover the loss. If the policy doesn't cover all of the loss, perhaps you could have them add a rider for the added value. I had to do that with my gun collection as they only covered $600 of a loss. My gun collection is worth around $6,000 and they had to add a rider. Of course riders cost a little bit, but at least you know they're covered.
Bill