One small tip. If you absolutely need to leave a guitar unattended in a tent - wrap it up in your sleeping bag. If a thief happens to crawl into your tent they might think there is someone in the tent and go elsewhere.

This is obviously totally insecure and doesn't protect you against a thief who has seen the guitar and decided they want to take it away - it won't fool anyone for very long. Best advice if you can't find someone to lock your instrument away for you is to bring it with you and mind it wherever you go. I know it's a pain but weighed against the risk it is the best option. Difficult to mind it all the time - there isn't that much room in a portaloo.