I would say there is something about the
tractor they really don't like. Maybe you will have better results with a house on the next batch.
Turkey's use running, flying and high perching for protection - you could always give them a run at roosting in a tree and see how it goes with the raccoons. You may have to train them to get started - At dusk toss them into the tree you want, and see how it all works out.
I'm not trying to be flippant here or inconsiderate of your situation. It's just that where I live we are over run with wild turkeys, and raccoons - and the system of roosting high up in
trees works for them. They have no raccoon problems once they are past the chick stage. Should something start to climb the tree the birds just fly out into other trees or a great distance away, and then up into something else.
This flying - running - roosting combo is all they need to stay out of reach of the coons. However, dogs can run faster than coons so that's a whole different story.
I've noticed that
chickens do not pick big trees and work their way to the top like turkey's do - it's really something to watch the wild turkeys at dusk. So for free roosting
chickens - I might add a watch dog just to give the coons more discouragement. This would also work for turkeys - a bird friendly dog with yard access will help keep the coons away.
I believe in the system the turkey's have going and this is why I'm suggesting working with the turkey's natural instinct, might be easier than building a house just now.
Or you could try some delicious food to entice them into the tractor, but I don't consider this a solution much, because it still involves you to work.
Sorry I don't have more suggestions....