I wrap them in news paper before freezing them and then put them in the truck the night before and most of the time they are thawed by the a.m. Of course in Florida thawing is not much of a problem and in fact we often go to the opposite extreme in that we will not thaw the birds before training to increase the lifespan of the bird, especially pheasants.
We do the same thing. Tuck head under a wing, wrap in newspaper before bagging in trashbag and placing in freezer.
Pull out birds at 5:30 AM and transport to field to meet at 6:30AM.
Place in wingers or hand throw while still frozen. Older dogs don't care and the younger ones learn how to get a better grip. By 10 or so the heads are all flapping away as the dog returns.
We easily get a couple of months use out of ducks when used 2 or 3 days a week this way.