I'd talk to his teacher about it. Will they do a presentation before hand explaining what's on offer, and stuff like that? Is it local enough that you could take him during the day and pick him up to come home at night?
My DD's school do a 2 night trip to a PGL place in June in year 4, she hadn't quite turned 9, but she was adamant she didn't want to go.
She's a total home bird, hates even being on holiday or visiting my parents, despite the fact that we are with her, and struggles a lot with anxiety, but at the same time she loves all the outdoors stuff so we came to the arrangement that she'd come home at night, I dropped her off in the morning in time for her to have breakfast with everyone else, then picked her up in the evening.
I really didn't see the point in forcing her to do something she really didn't want to do. She was so anxious about it that it was causing sleepless nights and nightmares so insisting she went was going to do more harm than good.
She's still a bit funny about sleepovers at her best friend's house but is getting better, she just wasn't ready for it last year. She has the opportunity to go to France in year 6 which she's coming round to the idea of.