Does it have to be an advertised "fly-in". An "informal gathering" might work better. I was once ,almost, a founding member of the "Victorian Sidecar Club" when all this Liability s**t came up. 20+ years ago!
Myself and others decided not to go ahead with the formal founding of a "club" but agreed upon the sidecar owners group.(no capitals) No members, with no association, or any other details. ....Worked a treat. Each was responsible for his own safety and well being. We had some great runs.
It appears to me that as soon as you advertise a gathering then you, (the organiser) become liable for everybody's well being, how much they eat and drink, how all the visitors behave, invited or not. every bit like a school outing. Literally. I can control myself quite well, but there are others that display reckless behaviour with gay abandon. I don't want to be held responsible for them.