Toileting

My son, who’s nearly 13, regularly has toileting accidents. It’s not every day, and sometimes we go 3-4 days without, but then we’ll have several in a row, sometimes 2-3 accidents in a day. He takes himself for a wee without problems, and generally accidents don’t happen at school, but usually in the evening, weekends, and holidays, which I’ve always assumed is because he’s out of routine. He wants to go on a school ski trip to the USA next year for 10 days, and I’m bothered about how he’ll get on. We’ve tried the vibrating watch but he keeps taking it off because he says it’s uncomfortable round his wrist. Any ideas? Thanks!