A.V.
I second Mabel's Labels.
I can't find the article now, but there was a swim mask found in a lake after being lost for 2 years. Still had the label on it!
I will suggest to not use Write Aways and to put the label on a dry plastic part (vs rubber or cloth) if possible. I have a tag mate on my DD's goggles for the pool. The Write Away label didn't stick so well to her PFD's cloth but I was told to reapply it to the buckle instead and we'll be testing that this summer.
You can also use tag mates and other labels for everything else he'll bring to camp - bottles, lunches, shoes....They make camp combos packs you might find useful. DD has outgrown many things before the label came off. I'm a big fan.