The "free of charge" and "donations accepted" is a little naive. Perhaps the better wording would be "for the cost of filming, period." You are going to find you are paying for a lot of electricity, utlities, upkeep (ie Paint), and damage (both outright damage and just run of the mill "we filmed and dropped a c stand against the side of the helm" damage). Since you aren't saying that people are expected to pay for what they use or to keep the bridge in filming quality, you can't require it...so people are legally able to say "tough luck" when you contact them and say they broke all the buttons off the Captain's chair and you want help paying to replace them.
I advise you to reword and to make sure contracts get signed...to protect yourself all around in ways you never expect to need it. I know a studio that got burned by a production company that borrowed the sets and never paid their $3k electric bill - and then stopped payment on equipment they rented. (which wasn't found out until the studio tried to rent equipment from the same rental place and then was told no because they stopped payment on "their" last rental. It took a lot of explaining and scrambling to prove that, although the equipment was delivered to the production's physical studios it was actually rented by another company...just to clear the production's professional rep - as that rental company had spread the word around and they were, in essence, blacklisted because of the people who "borrowed" their sets.)