I once asked a county conservation director if our nudist group could have an event in one of the parks. He pointed out which one would work and said he would direct the ranger on duty not to go there if we told him what weekend. We said we would post a sign indicating private event and suggest no visitors in that area. The picnic went off without a hitch.
Asking if free hiking or skinny dipping is permitted is not a good idea for two reasons. 1.) It is always easiest and safest for the person being asked to say no, even when that's not the correct answer. 2.) Once you've been told something is not permitted you can't do it and then plead ignorance. And when it's a matter of law no government bureaucrat will take a stand on what is, or is not legal. Only a court can make that decision.My few experiences with park rangers have been good. When they indicated that nudity was inappropriate I got dressed and that was that. At other times nudity was not a problem. As you get further from civilization your chances of encountering a ranger decrease, and when you're in remote areas with no cellphone coverage anyone who might want to report you for being nude would have a hard time doing so. People I've met on trails have never indicated that they had a problem with my lack of attire, but I'm ready to cover up when necessary, and I'm non-confrontational.
I agree. Although the old saying "It is easier to ask for forgiveness, than for permission." is often misapplied, I believe this may be a case where it is prudent. I have hiked naked and skinny-dipped in various locales, on both public and private land. for nearly forty years. I have had days where I didn't encounter anyone, and days when someone happened along. I have been politely but sternly instructed to get dressed and be on my way, I have been ignored, and have been laughed at, cussed at, scolded, told to watch put for others, and everything in between. I have encountered private citizens, as well as LEO's and other authorities. I have never been detained, arrested, or charged with anything. I have been alone, and with company. I believe that there are a few issues to consider: a) stay away from popular or frequented areas, the fewer people around, the less likely to cause offense. b) be aware of your activity -- simple skinny-dipping is generally considered harmless, having sex (which I think is natural and fun to do outdoors as well, and I have been "caught" a few times) should be undertaken only in the most private locations. c) the attitude you present will often dictate the outcome of the encounter. If you are approached by anyone, be polite and respectful. It is usually best to start finding some clothes and putting them on -- whoever you've encountered will generally tell you right away if they don't mind and intend to allow to to continue your activity naked. And if they ask you to get dressed and go, do so; if you feel you are within your rights you can always appeal and petition your cause later, but escalating an encounter will just engender negative responses and ill will toward you and the lifestyle. That's my three cents.