I think most household insurance policies cover for theft from sheds. If not then you could change to one that does or amend your own. You just have to work out what it is worth to you to see if it falls within the insurance cover. Purchase price, anything you have spent on it and what it would cost to replace should you need to. Keep an eye for adverts to give you an idea of sale price. I like that, would like one myself, that’s the trouble with looking on this forum. Got enough projects already.