I have transported many cats for rescue groups on multi-day trips across the country. If you crate them for travel, you can use a disposable 8x8 aluminum baking pan for litter. I prefer feline pine--put in just enough to cover the bottom completely, and either toss the sawdust at stops, or toss and replace the whole baking pan if needed. If you aren't crating, I would recommend a litter pan in the shower, and locking the cats in the bathroom during travel. If you put their normal bed in the bathroom, they probably won't mind curling up and napping the trip away.
I do not have experience with cats and the electric sofa or slide, so I will defer to others on that issue.
Happy Traveling!