Stop feeding them 2 days in advance, you don't want excessive ammonia in the water. There's a sedative called finquel, you can order if off ebay, that slows down their breathing for travel. They pull out of it as soon as you put them in fresh oxygenated water. There's also a water additive called Bag Buddies that conditions the bagged water for travel. I use the large koi shipping bags (available online) and put only enough water in it to cover their back dorsal fin. I "have" used large tubbies in the past, but depending on your driving skills, they can get a bit sloppy.
They do make battery operated air pumps...I had a solar one that I used for a short trip (taped the small panel on the window) I know the sedated fish can make a 2 day shipping trip. There are also small tablets that you drop in live bait wells that fizz and make oxygen. You have to get those from the bait stores, but I've never heard of anyone using them for koi transports. I've seen small pumps that you can plug into your lighter, but don't know where you get them.
Every now and then you can get a pet store to agree to ship them for you for a fee.