My previous bunny Nibbles wore a harness (current bunny Porky refuses) very happily, and I took him on nice long hops around the neighborhood, I would not have tried it on a trip though.
First off, he chewed through several leashes (I eventually got him a chain one.) This wasn’t a really big deal since we were close to home, it just meant He got carried home instead of getting to hop home and eat clovers. If I had not managed to pick him up, we were close enough to home that he would have been able to find his way back by himself. Worst case scenario, I could have put up lost bunny posters. Far from home at a rest stop it’s a totally different situation, It’s much more likely he would have been stressed and unwilling to be carried back to the car, and it’s not like he could find his own way home safely, and you can’t spend weeks at a rest stop looking for him.
Rest stops are dangerous stressful places. People are walking dogs. Cars are pulling in and out. There is garbage everywhere. Who knows what pesticides and herbicides are sprayed on the lawns.Not a good place for a bunny to hop around.