My concern is in an emergency situation. If you have an accident, etc., while on the road, do you really want to be spending 10+ minutes trying to capture your cat and get him in a carrier? Or would you rather just grab the carrier with the cat in it and get to a safe place?
For me, I prefer a cat or bird to be confined in something so I can get them to safety. My two dogs aren't going to "go to ground" when scared like cats and birds, so grabbing them by the collar and attaching the leash will take only a couple seconds. Trying to get the cat out of a hidey hole while your RV is stopped dead in a dangerous position, is not something I want to do.