My tips, as a parent having had more than one child with incontinence issues who regularly go on camps etc are as followed:
Wear fleece pjs as these will be more absorbent than other type of pjs. This only works if child is not a “hot temp” sleeper as will be uncomfortable otherwise. Take spare pjs with same design so other kids do not notice change in clothing.
If won’t wear fleece buy dark coloured pjs so not as obvious if wet self.
if they are sleeping in sleeping bag, can you send him with a spare identical one that staff can swap out whilst the other is washed/dried?
I highly recommend Brolly Sheets Waterproof Sleeping bag liners. They’ve been an absolutely godsend when ours have slept away from home. You can find them on Amazon. They aren’t cheap but do add an extra layer of protection against the sleeping bag getting wet (as long as don’t wriggle out of it!) If other kids ask about the liner, mine just say it gives an extra layer of warmth and help to keep sleeping bag clean.
Ypu can get pants that are for incontience but most won’t hold a full wee. I’m yet to find one that works for my mine who go for it big time, and sleep through it!
Mine took pull up pants (can get older sizes) that they packed inside pjs and spares were inside wash bag/suitcase easily accessible but not obvious to other kids they shared with.
Let staff know your child potentially wets the bed, and ask that they can ensure child has access to shower if wets self. Let your child know which staff they can approach for support if needed.
You may find your child is ok, as often when away from home less accidents happen.
Might be worth checking out ERIC website to see if they have any other recommendations.
Hope your child has a great trip.