Don't worry about it, and move on to the next buyer who doesn't ask dumb questions.
There's a carfax because there are a million-bajillion cars on the road and you can charge a million-bajillion people $35 each and make million-bajillions of dollars. By comparison let's say there are 100,000 truck campers out there (I think I'm being generous at that number). You'd have to charge $1000 per camper to make it even worthwhile, and the bean counters know that nobody is going to pay that.
The creators of carfax didn't do it to be nice. They did it to make money.