So far the story looks great, especailly the fact that it's in a shorter time span than At the Cabin and that they are on a school trip; it will make the situations in which they find themselves more interesting, such as trying to have sex without alerting other people. It's also great to see that now Vicky is the one having a crush on Zack, while he has a crush on Natalie; i'm curious to see how the whole thing will play out and how will Zack end up with Vicky. Also, it's great to see that Chloe is a lesbian, this way she can go after a girl (Lisa) and everybody ends up with someone at the end up the story. I am curious to see how will Chloe and Lisa will end up together considering that Lisa is Zack's ex-grilfriend and so far she has been portraid as being straight. And i'm glad to see that Gavin will end up with Heather (if you don't decide to change that).
As for what i expect to happen, i imagine that Zack, Victoria and Natalie will for a small "love triangle" for some time, until Zack and Vicky end up together. I think that a possible out come would be for Jake and Natalie to end up together. As for Gavin and Heather i imagine that she will tease him mercilessly and once they get together she might push him to have some exhibitionist sex or at least in a place where they might be seen or heard.
Good luck and happy writing.