Look for oportunities in the future to casually pick up the discussion. In most cases you won't be able to convince somebody to try it right it away. Give it time. Private resorts and parks are better than a public beach for an introduction. An initial experience that is a bad one will be more difficult to overcome.
Free beaches offer little security, convenience, or legal protection.
Start small and work toward a visit to a resort or park. If the concept of being nude more than clothed is new, then don't try to force a trip to a resort too quickly. Start by getting accostomed to being nude more and more often around the home. A group may be easier than an individual. I was friends with that we go skinny-dipping in Lake Michigan.