long-distance move, how to travel?

My boyfriend and I are moving from Savannah, GA to Portland, OR (about 3,000 miles or 5 days in the car). We're both drivng our own cars and taking our own cats.
His cat, Casey, is horrible in a carrier, and so he just lets her crawl around in the car (seriously, she claws at the sides until her paws bleed and thrashes around violently.)
My cat, Bailey, has never been on a car trip longer than 20 minutes to the vet and back. She's great in a carrier and seems to just fall asleep. I have a very small car and don't feel comfortable letting her ride not in a carrier with me (she's only 1 year old and still moves around excitedly like a kitten. I'd be terrified of driving with a loose cat to distract me).
What I need to know is how to handle her on the road. How often should I stop and set out a litter box for her? How should i feed/water her on the road (she's used to free feeding/water here at home). Does she need like a leash/harness thing? What should I avoid? I'm trying to drive 15-hour days to beat the moving truck to Oregon so I can find us an apartment, is this too much for her?
I know i'll have more questions when I get to Oregon (where to put the food, litterboxes, etc.) but right now, i'm just worried about getting all four of us there safely and happily.
Anybody made moves like this with their cats?

You can put them in the rear of your vehicle, but you need to put up a barrier to keep them there and to keep them safe. You can go to a Petsmart and look at their selection of vehicle containment shields and decide which is best for you to use. Or what you can do instead of putting them into a dark closed carrier, is put them in a cage (if they get along) this way they can see out and not be so confined, but be sure you get a large enough cage and not one where they can stick their head's through the bars. You pad the bottom of the crate, cage, or back of your vehicle with puppy wee pads or disposable diapers, and you don't worry about stopping and letting them use the litter pan- they will be to stressed anyway. I wouldn't feed her before she travels in case she gets sick, but I would get those attachable bowls and put those in the carrier or cage and fill them without opening the cage door up and the possibility they could escape. get a breakaway collar with an ID tag or microchip both cats before leaving.

You don't have an apartment yet in Portland? Did I read that right?

oh, dear one, I feel your pain!! I just moved from Nashville to western MT last month with two cats (among other creatures). I would encourage you to follow Hissy's advice, lord knows she's much more experienced in transport than I am, but let me tell you about my experience, briefly.

1) BE SURE to stop food several hours before you plan to travel. I let my girls have breakfast two to three hours before we left, and Bella literally made herself carsick; she yowled continually for the first 90 minutes until she vomited. Best bet, feed them in the evening ONLY, but offer water overnight and at regular intervals along the road.

2) I did invest in figure-8 harnesses for the girls, but if you have a ballistic cat I would advise against it. Bella was always a bit of a nervous nelly, but we had her out on leash at one point and she attempted to crawl up in the engine compartment of the U-haul (might have had something to do with her slight build and the outdoor temp of 40 deg F, but. . .) Better safe than sorry.

How far has Casey travelled in the past? As I said, Bella was always a bit nervous on the way to the vet, but after the first day's events she settled in within 15 minutes on the road and slept most of the way. You know your cats better than anyone, but I know others' accounts were invaluable in our survival of the trip.

Almost forgot. . . Fifteen hours is a really, really loooooong travel day, even without pets. remember you will need to unpack for the cats, too; litterbox, food, beds if you choose, and make sure they make it safely into the motel room. This takes a lot longer than just carrying your bag, and you will not have as much time to sleep as you might think, by the time you feed them and settle in for the night. On such a long trip, you do NOT want to cut yourself short on your sleep!!

I also found that after 12 hrs, the cats had lost all patience w/the carriers and were incredibly thankful to be on solid unmoving ground, even if it did smell completely foreign.

i'm planning mostly 8-hour driving days. I have to beat the moving truck there, and my boyfriend is getting there a day ahead of me. we were going to fly up and look at apartments/houses but until about 2 weeks ago we were planning to move to new york and we spent a ton of money flying there and looking for places and jobs only to discover we really didn't want to live there.
the day after the night i get there, we have an appointment with the realtor and a great vet that will keep them for the day while we look for a house, or one of us will go look and one of us will stay with the cats.
i really like the idea of a big cage for bailey in my car (casey is going with him), and thanks for the advice about food! sick cats would be very icky in the car.
casey has traveled (not in a carrier, just in the car) 1,000 mile trips with the bf from savannah to new hampshire in the past, so i'm not worried about her. plus, they'll be in a different car, taking a different route and 3 more days.