Wild camping

(This is a fantasy my wife and I have) A couple in their 40s go camping. They set up their tent on a cosy campsite with just a couple other tents. In the first night, the woman wakes up from noise coming from a tent nearby. The woman sticks her head out of the tent and looks where the noise (moaning) is coming from. Then she sees a shadow play on one of the other tents and she clearly sees another couple having sex. She gets aroused and starts masturbating. She wakes up her husband and they have sex. The next day the couple plans on doing the same thing as their neighbors. They set up a lamp in their tent at the right angle so they can do a shadow play on their own, hoping the other couple will see them. It works, the other couple sees them. And the neighbors go to investigate by going to the other tent and they try to take a look inside. They manage to do that and both get very aroused. Then they get noticed by the couple but are welcomed in the tent and the two couples both have sex next to each other.