Our newest family member is coming up on four months old and is 'in training' on many levels. We have made it a point to take him with us as much as possible when we leave home to run errands. As a result, he is very comfortable riding in vehicles. Usually curls up on the center console and goes to sleep. Harness on, and leash locked in to seat belt just in case - although he has never tried to make a break for it. He has never seen the inside of a cage.
We *always* carry him in/out of the vehicle. He is never allowed to 'jump down' when we get home or anything like that. We want him programmed that the only way in/out is being held. Same thing applies to the camper. Going through the door himself isn't in the realm of possible options in his little mind.
We have had one camping night so far. He took it in stride. Litter box in the shower, food under the table, and he couldn't have cared less. Typical feline attitude - "No problem, I can run this camper just like I run the house". The camper will be coming with us for family Christmas so we have our own quarters, and that will be his second camping trip.
Our previous companion (RIP) was much the same way. He loved home, and tolerated travel / camping. We have to drive through some trees to get to our house and he always identified that as 'homecoming' and would get excited to go back to his house. It created a number of comical false alarms when there were trees coming in to a campground, LOL! He would 'talk' a bit about leaving home, but eventually learned the lesson of futility and got quiet after the first five miles or so.
I think the trick is to get them used to riding in vehicles at an early age. And not just to go to the vet either. Car trips should just be another day for them, and not anything unusual. We didn't start the previous one at an early age and the first car trips were the under-the-seat howling panic, whereas the current one has been in a vehicle at least a dozen times in his first few months.
All in, we very much enjoyed camping with our previous companion. After we lost him in February 2017, I think we only went camping twice over the following two summer seasons. The camper was really sad without him. With the new kid, I am looking forward to going camping more often this coming year.
-Eric