From everything I have ever read about this topic, and from the very few occasions I have been exposed to such things, being a nudist doesn't really have anything to do with sex. Which is why, people in nudist camps don't usually have this problem.
Again, from what I have read and come to understand, wanting to be nude and a nudist is a lifestyle choice. It's about freedom to be completely open and who you are as a person.
I know the few times I have been around others, and actually it was even in a med fet situation, a few of us were naked together and all of us were quite comfortable. No one was erect. Actually, to be 100 percent honest with you, it was quite nice, and not sure this is a word or not, but quite freeing to be able to stand around totally naked, in front of both sexes and having intelligent conversations.
Erections happen, with clothes or without. Since I do not have a penis I can't even begin to fathom what triggers them, and how you untrigger them. I know for some younger guys, the old addage is, "if the wind blows too hard" they get an erection. I also think age in general in a nudist type of place would also have a lot to do with it as well.
But again, from what I read, I would assume that having an erection while at a place like that would be bad form, especially if the man was being inappropriate, because as I said earlier, being a nudist isn't and doesn't have anything to do with sex.