Plenty of room for a 3 day drive of 1600 miles. Three days as we are not young and didn't want too much time on the road every day. I drove van, husband drove the U haul.
Built panels with pine 1X4s with 2X4 (size of the opening in the wire) fencing panels attached. Took out 2nd row of seats for more room so I could get in to feed and change water. Put spacers between plywood bottom of cage and floor of van. Husband built a little 'drawer to fit in the space under cage for litter box; cut rectangular opening in floor over drawer so cats could potty, litter could be contained rather than loose in cage, and we could clean out the litter box without cats getting loose, one of the cats could get pretty hostile about being moved. Did not want any escapes!
Put a cardboard box with cut outs in cage for cat hideout. One cat spent a lot of time in the box, with his blanket, more blankets and a towel in the rest of cage. The killer cat enjoyed being on top of the box and watching the scenery. They hollered a bit the first 50 miles then gave that up, realizing it was not getting them out. Killer really enjoyed the times we drove along side rivers. She was fascinated with the sight of rivers. Who knew?
Had 2 way radios so we could keep in contact on the long drive, and make sure each driver was awake. Whenever husband called on radio, killer cat would start looking around for him in the van. Pretty funny in the rear view mirror on lonely stretches of highway!
We did pick up cat tranquilizers from their vet before moving, in case they really had trouble traveling. Did not need the pills until reached destination & I had to get them out of the cage and into the new domicile. Knew one would come easy as he loves being held tight. Didn't want to chance Killer shredding me, as happened at Vet's office when idiot assistant didn't listen to husband telling her to let me get Killer out of her carrier. Definitely did not want to risk losing my grip getting her from cage to carrier and into the new home. Little dose of tranqs in some food, wait a bit, easy and secure move.
We had planned camping out each night, so right there with the van/cats. But it rained like hell nights 2 & 3, monsoon season out here in the west, so we gave in and got hotel room. Cats were fine in the van overnight. One of them had been a feral kitteh, so he was OK sleeping in the van cage and he kept Killer calm.
Important reminder re moving cats: if cats are not 100% indoor cats, keep them inside new home 100% for at least 2-3 weeks so they understand this is their new home.