I can honestly say that, as a teacher, I doubt any of my male colleagues would be willing to sleep in the girls' area, for fear of accusations.
I've worked with two young male teachers over the years who did turn out to have an inappropriate interest in teenagers (both discovered & dismissed, one of them prosecuted) & their actions have cast a long shadow over an entire teaching staff
.
It's just the norm on trips that female staff go into male sleeping areas, no problem (eg. recently I had to check on a 12yo lad at intervals throughout the night because he has a health condition that needs monitoring), but no male member of staff would dream of entering a girls' room without a female colleague. It's so ingrained in the culture that it's never even discussed, we just get on with it.
Also, as pointed out upthread, male volunteers are harder to come by. I aim for quarter to a third male staff if I'm running a trip, & I have to twist some arms.
Family excursion is entirely different; seems sensible that they have a family section.