There might be a different way to attack this issue. It will take some time, but the pay off will be tremendous.

I know you mentioned you don't have an problem with his weight, but if he lost 60lbs (to start), I think you'd find his confidence would dramatically improve. Eating healthy food and regular exercise doesn't just make you lose weight, it also changes the chemical reactions in the body and makes you far more positive.

Yes but they don’t have time for that for this trip. In the long run this is a great goal for couples to do together as they will both feel better, be more positive, and usually get a performance boost (for both partners) in the bedroom.

I say for this trip take things slow, he can strip down while sitting and then he’ll soon see that everyone else doesn’t care and there are a variety of people around. But depending on how much time before the trip you two could start on Duran’s advice.

Get him to lose weight so he is less bashful. Do you cook for him? Pack his lunches? It's up to you as much as it's up to him.

Obese with nothing showing
 

I am obese and can relate to this issue but my wife and I really enjoy the nudist clubs we have visited across the country. She is beautiful and enjoys men looking at her secrets.
I have always been anxious about the appearance of my cock but my wife knows the truth. At our favorite nudist club we woke up with a loud fuck. One of our neighbors said we woke up half the club.
That afternoon, a lady sneered and told my wife we sounded like she was getting it from John Holmes. My wife looked around to make sure no young people could see then she dropped to her knees and began licking my balls followed by taking my growing and appreciative penis into her mouth. When she pulled back her head her hand was pumping a not quite 6 inch cock but it was really thick and that is what she loves.
We cannot walk around family nudist clubs with hard-one, but we know the truth.

hi
 

has it occurred to you that he is small against the background of a large body? If a man is skinny and narrow in the pelvis and hips, his penis seems big. But in fact, no more than a large man with a broad bone.