We have a cat that became a camping cat at age 6 weeks. Jerry will be 7 in April and has traveled many times to other states. He is a fantastic traveler - loves to look out the windows
while traveling, uses his litter box and will eat and drink while we are driving.
He has always worn a harness and is on a leash always when we travel - which works well.. but honestly, a cat can get out of anything. We always make sure we never get in front of him while in his harness. A cat will just stop- and back up and out he comes - harness on the ground and it's not a good thing to have to try get him/her back. Jerry has backed up out of several different harnesses - the one we have now seems to work but we still never get in front of him.
Having your cat along can be fun, but we never leave the car running when we aren't in it. If we want to eat, if it's too hot out and we can't leave the windows
open a little for air for Jerry, then we go somewhere where we can eat in the car. We also use a small stroller for him - makes it easier for us to enjoy sight seeing.
My only concern for your trip is what will you do with your cat while you enjoy Disney, Universal etc? Leaving a pet in a trailer would be the best, but a few trips back to the trailer to check would be good.
Have a fun time and enjoy traveling with your cat.