[anonjohn]

It's usually the other way round, male-female couple-wise. Here are some thoughts transposed from shy self-conscious women and naturism.

He is probably happy when you are happy and that might be enough for him to agree to your going to this resort or beach. The only safe "reward" or "incentive" is some other place/event nearby which he might enjoy. Unrelated Incentives/rewards/punishments might put pressure on him and cause a counter-reaction.

If he feels that his nudity is completely his choice then he is more likely to play ball. If you are natural, relaxed and matter-of-fact when you are there, it will help him.

After you get onto the public beach or resort he (while clothed) will see plenty of men with a smaller penis/bigger belly/smaller muscles than him who are completely unselfconscious and unaroused.

Once he experiences that most men are not built like Greek gods or porn stars, he might start to reframe what is normal and acceptable for men. Then to think he is OK as he is. No doubt you have been affirming and appreciating his body (especially the parts he is anxious about) at other times!

Genuine naturists/nudists (I don't know about swingers) are much more body-accepting and less judgemental about appearance than the general population. They don't see social nudity as a beauty contest or an opportunity for exhibitionism or showing off.

After about 10-15 minutes when he has got over the initial shock of nudity he might feel comfortable with experimenting with feeling the sun all over his body of the freedom of swimming naturally. But he must make that decision himself.