I would recommend for you to take your cat on short car rides to get use to the car. Also maybe not even having her travel in the crate might make them more comfortable and like that maybe you can make a small litter box for her.

I would absolutely get a harness for her. My cat is an indoor cat as well, and I always put her harness on anytime we leave the house even if she's in her carrier. You never know if the carrier door might open or she might try to run out the front door while you're taking other things to the car. The harness makes it really easy to snatch her up if she tries anything. Also make sure she has a name tag on the harness with your phone number in case, God forbid, she escapes. The harness won't come off, so it makes it easier for someone who finds her to catch her and call you right away.

As far as traveling with her, 4 hours really isn't very long for a cat and she should be fine without a litter box for the trip. Just think about how often she uses the litter box throughout the day at home, I'd bet she uses it less than every 4 hours. Plus, if she's not drinking anything for those 4 hours she should be fine.

I'd suggest that when you get to your destination, leave her in her carrier in the house for a few minutes and set up her own little area inside the new house. Make sure it has her litter box, food, water, and a bed if she uses one. Have it in a corner where she won't be too bothered by the commotion of moving. Once it's set up, take her directly to her new area. Let her out so that when she leaves the carrier, she can see her familiar litter box and food/water dishes right away. She'll probably head straight for the litter box and then hang out in her new area for a while. I read somewhere that a cat won't feel comfortable exploring a new surrounding until they know where their "safe place" is, which is usually the litter box. They know no one's going to bother them in the litter box and it smells like them, so it makes the cat a little more comfortable. When she's lurking around and exploring her new home, make sure there aren't any loud noises or sudden movements to startle her. Let her explore quietly alone.

That's what I did when I moved my cat and she did really well. Not sure if your cat wears a collar, but as soon as she's done with the litter box I'd take the harness off and put her collar back on. My cat doesn't like her harness but I make her wear it anyways because it's safer for her. As soon as I take the harness off and put her regular collar on, she's right back to her old self.

Good luck! 

I have worked at vet offices for 6 years now. I would recommend you also try pheromone treatments, like a NurturCalm collar, to sooth the cat and make the move easier on all. They release a pheromone that is similar to the one released by the mother while she was lactating, it gives a calm soothing feeling to the cats. It usually takes ~48 hours for it to start working. Each collar last ~30 days. The Collars ~$15-20. I also agree to start with short car rides also.

First, congrats on the job to him! :)

As for your furbaby, 4 hours in a car will fly by. I've moved my two cats probably 6 times in the past 5 years. 3 of them were 4 hour trips (moving them to/from school at the end of the semester/year) and the other 3 were long distance moves, 2 with hotel/overnight stays in other places. I bought scraps of fleece for their carriers to use as blankets - get extra just in case it gets dirty/smelly.

One of the best things I've done is take away their food about an hour before we leave. I know it seems mean, but my "oldest" WILL throw up within 15 minutes of being in the car. (I've tried driving around for 20 minutes before I leave... and she doesn't barf then.) Take away the food, and she's good to go. I let them have water. During rest stops (as long as the weather outside is ok) I let them out of their crates, put water out, and pull out the litter box, just in case. Then I'll take a nap or get a quick snack, and hang out in the car with them.

For the new place-take a blanket that your cat regularly sleeps on and pack it-unwashed-and then bring it out in the new place and set it up in a corner away from a lot of traffic so she can get used to the space on her own. Put out some of her favorite toys and create a "safe" space for her where no one can bug her.

 As far as the harness goes, one of my cats LOVES it, the other one would basically (based on her reactions) die than ever be put in one ever again. So, it's worth a shot. Just make sure you get one that she can't pull herself out of. Cars and dogs and strangers and who knows what else may startle her, and she'll try to pull out of it. I wouldn't recommend trying out the harness for the first time while moving her for the first time, though. Lots of stress at once may not be the best for her. If you decide to get her a harness, put her in it for 10 minutes and love on her. Let her know it's okay and give her treats. Do this for a while, adding time onto the "harness sessions" don't attach a leash-and make sure you're watching her the whole time. She'll get used to it eventually and then take her outside gradually. New things are terrifying for some kittens.

 (This is all from my experience as a cat-owner. I grew up with cats (have had 4 throughout my childhood) have two of my own and I have 2 "nephews" and 1 "niece" .) Feel free to message me if you have any cat questions! 

I've transported too many cats 5+ hours in the car. The only time I've had a cat pee in the carrier or get sick was on in-town trips surprisingly. I use a hard carrier with a towel in the bottom. I feed the night before but then do not feed again until we get to the destination. Water is offered every time we stop. We set up a litterbox on the floorboard of the car and when we stopped we'd put the cat in the litterbox, give it a chance to do it's business and then put it right back in the carrier, keeping the doors closed the whole time. Your cat may cry but she'll be fine once she gets to her new home.