Here's something close ...

Fun at the Cottage » by browneyed_

A family is staying at a relative's big old cabin on the lake. I wrote a couple of threads, and would love to see others contribute more. Basically, the scene is set for the oldest brother and the oldest sister to fool around, and the younger brother and youngest sister already have had sex.

I'm thinking of threads where the older sister watches the younger siblings in action, and then has sex with one or both of them, too. Also, the youngest brother might be fun to match with mom... anyway, lots of potential there.

As for actual camping out - with tents and all - give me time. That could be a fun setting.