I’m a CPA (Florida) who works with not-for-profits. In general (disclaimer: this is not specific advice to any group), a club can be formed inexpensively, and the IRS does have some a new processes in place for small non-profit clubs and educational groups. They do not require official formation at the state level until they get bigger. However, I’ve also seen groups get shut down for not doing it right. See if you can enlist the aid (give a membership to a CPA) or pay a consulting fee to a CPA for to get the right advice. I agree with the liability suggestions above. DAN (Divers Alert Network) is a great place to get information specific to your group, along with a local attorney in your state for the right wording in your waiver.