I've been working on harness-training my cats in preparation for the move because I worked out that there was no way I could keep them all in the carrier for the duration of the seventeen-hour drive. Instead, they will wear their harnesses and be restrained with leashes anytime I open the car door.
So far, the training is...interesting. My two older cats are fairly relaxed about the harness itself, but the leash still wigs them out a little bit. But my little girl is not pleased by the harness. She walks around like she's crippled, even though the harness doesn't obstruct her movement in any way, meows pitifully, and is generally not happy with the situation.
My basic plan is to get them used to wearing the harnesses for longer and longer each day until they're completely relaxed in them, then do some leash work. All this is supplemented by lots of petting and treats, naturally.
Overall, the thing I'm dreading most about this move is listening to these guys cry for seventeen hours and trying to keep them contained. My mortal fear is that one will escape during a stop for gas, and I just couldn't handle that, but I think with the leashes, everything will be okay.