Here's my very sad response to your "camping" question.

Many years ago, I had Shrimp Boat, who was a rescue female that I found at a seafood market in NC. She was about 4 months old when I found her. I loved that cat dearly, and would have allowed her to be an indoor/outdoor cat if she had preferred. But she didn't prefer. She wanted to stay inside.
That was fine, but I missed her when we would go camping on the weekends, and I felt guilty leaving so often. So, one weekend, we were headed to a state park in the mountains of SC, and I suggested to my husband that we take her with us. We had a yellow lab that was going as well. She was a great car rider, but when we got to the state park, it was dark, and she was nervous. I took her out of the car and put her in the camper, while we were unloading. Unfortunately, on one of our many trips in and out of the door, she shot out like a bullet. We searched and searched. In fact, I slept in a lawn chair the whole night, hoping she would return. She never did.
That was the worst three days of my life. She was tagged with id. We put up multiple signs, plus knocked on the door of every trailer in the campground.
Bottom line...we never found Shrimp Boat and to this day, I feel guilty about it. She was about six years old when this happened.
I didn't try a harness with her, and maybe I should have. But what I really should have done is leave her at home!!! It has been since 1989, and I still feel a terrible guilt about what happened to her.
We adopted Mimi two weeks later. I still have her and she NEVER goes on trips.
Logan