My brother and sister-in-law wanted my wife and I to go with them on a two week trip out West. We would be camping most of the time to save costs. We all drove in their car and used my camping equipment.
We spent the first night in the badland camping in a remote area and having to take solar showers nude in front of each other. Everyone was ok with this and we left our inhibitions back East.
The next day I was driving across Wyoming and I noticed that something funny was going on in the back seat. My wife was sleeping in front so I adjusted the rear view mirror and watched my sister-in-law stroking my brother-in-law.
Later, in our tent, when I told my wife about what she had missed, she pulled out my cock and jacked me off on the spot (this was going to be a good vacation). My wife and her sister seemed to have a little competition still going on!!
The third night we stayed in a motel room with two double beds and after everyone had showered we stroked and played with each other, with the bathroom light on and you could see everything that the other couple was doing.
Another night in a campground my wife was giving me a stroke in the tent when they walked in and she didn't just carried on and I came hard. They went to bed and there was enough light to watch them have some sex time.
This went on for the entire two weeks. Both of us guys had more hand jobs and sex than we were used to and couldn't wait to take another vacation together.
Years later my brother-in-law loves to talk about that trip and my sister-in-law told me that she had no idea how BIG I was until that trip.