I have to drive 400 miles and back with a large cat and hoped to find some sort of car cage or carrier that included an upper sleeping shelf and a lower level for litter, food and water. Anybody know of one? Haven’t found one yet online. Thanks!!
When I transported my two cats here from NYC, over 450 miles, I put them in cages without litter, food or water. I had withheld food and water for several hours before the trip, and they did just fine. Didn’t even complain.
When I first found my cat and had to keep him safe from the dogs for the first couple of days, he lived in a dog crate. I put a plastic milk carton on its side in there so he had a cozy area inside the carton or could perch on top of it. Litter and food went in front on the bottom. If I was going to do something similar for travel, I would just zip-tie the carton in place so it didn’t slide around.
I couldn’t find anything like what you describe, Napier, but I am curious. Does your cat need to be caged while traveling? When I moved from Georgia to Kansas and then from Kansas to Idaho, I traveled with four cats. I kept a carrier with the door removed in the back seat so they could go in if they wanted, but I don’t remember there being any takers. (I also leash-trained them though). Never had a problem except one time at a rest stop when a truck driver blew his airhorn and startled one enough to bolt right up my leg and chest to my shoulders.
I took a trip about half this far, 250 miles, and the first time I let my cat have free roam of the SUV with a litter box in the back. She never used it, or even tried. She just laid down on the floor of the back passenger seat the whole way. On the way back I thought to myself, ‘This is crazy, what if I have a medium accident, or get stopped by the police’. She could easily bolt out of the car and I’d never see her again. 
So I left her in a large crate the whole way back. No food, water or litter, and she did just fine. She slept nearly the whole way. Next couple of times I took this trip I did the same thing both ways, leaving her in the crate, and she was perfectly content. She complained for the first few minutes then she just settled down and slept. I had the crate facing forward in the back seat so she could see me, and that was enough. I had my arm on the center console and halfway thru the drive she reached out thru the bars of the crate and tapped my on my elbow just to remind me she was there. 
I’ve done similar trips, and I leave food/water/litter out of the crate while driving and either put it in when I stop for my own pee/snack/coffee/gas break, or if the weather’s cool I’ll crack widows a half inch and just open the crate door to let them stretch a bit. Kind of depends on the cat(s) and the weather, and the general set-up of the car and occupants.
But the cats should be fine for one 6 - 8 stretch with limited access to food/water/litter. Unless they are season travelers they usually just hunker down anyway.
I suppose it might depend on the car. Some friends who took their cat to Spain (>1000 miles) had a hatchback. They made a fence out of chicken wire, put half the back seat down and the moggy had plenty of room in the back to move around. They had a lead and harness for ‘comfort breaks’.
I agree with those who say this distance really should be fine for most cats (ones with diabetes and/or kidney issues might require different strategies) just crated for the duration. I used to make a trip of about six hours all the time with two cats. Never any issues or accidents.
Take up their food and water a few hours before leaving. Clean the litter boxes shortly before leaving. This always inspires my cats to go pee. 
When traveling with any animal, the animal should be secured for its own safety, and yours.
Yeah, nothing like having a cat get under your feet while you drive.
… or sleeping in your lap when you have to slam on the brakes … ouch …
Thank you everybody. I especially like the milk carton on its side.
This particular cat is diabetic and gets insulin every 12 hours. I’m not sure how critically he needs access to food, water and litter (our vet knows our plans and didn’t mention anything and I didn’t think to ask).
I certainly want to protect him by confining him, as having him get out and run off in terror would be disastrous for him and me. I wish we did not need to travel with him at all, but last summer our specially trained house sitter was unable to give him insulin as he fought her off, and I wound up turning around after our first night there and spending the vacation at home with him.
With a diabetic cat, he’s a little less likely to be able to hold it for 6 hours.
If he’s a good traveler, you could just put him in a crate, then halfway there do a stop where you let him out to use a litterbox and get a drink.
If he’s a bad traveler, he might not be willing to do that. Of course, a bad traveler is also less likely to drink/eat/use a litterbox if it’s in the crate with him either.