Cetawin, I think if I was doing the moving and had a van I would:
Get some dog kennels (they have solid bottoms and poop won't get all over) and put as many chickens as you can fit without hurting them in each one. And some for the ducks. I bet you could get by with 6-7.
Then I would buy one of those portable break-down crates. Every 4 hours or so, you could take a couple of the dog kennels and put the birds that are in them in the portable breakdown crate that you have already put food and water in. (bring spare, clean empty waterers just for that) give them 20 minutes or so while you stretch your legs or have lunch and then put them back in and rotate the next bunch in 4 hours. Then everyone gets food and water several times a day. Yes they will be miserable, but they will be safe.
It may take a few extra hours of time during the total trip, but you would know that everyone was safe. It will get stinky though. Bring lots of paper towels, spray bottle and garbage bags!