Dunking, or scalding, is pretty much how it's done, from everything I've read and watched on YouTube. When we processed 16 chickens last fall, we had a turkey deep fryer outside with us (the kind that sits on a propane burner) and a thermometer to monitor the water temperature. We kept it at about 125° - 130°. Dunk the bird in and move it up and down, up and down, up and down. Pull it out and try and pluck a large wing feather. Does it come out easily? If so, then hang it by its feet and begin pulling the feathers. You'll be amazed at how easily they come out. You can just run your hand from its ankle upwards (or downwards, since he'll be upside down) and all the feathers will just slip right out. If the tested wing feather doesn't come out easily, dunk a couple more times. Be careful not to leave it in too long or the skin will be easily torn.
Scalding the turkey at this low temp will not affect the length of time it can be left in the freezer at all. "Hard scalds", which are at temps of about 160° can shorten the time the meat stays good in the freezer. Another thing that affects how well the meat does in the freezer is how quickly it is frozen. Slow freezing will actually dehydrate the meat at bit. The faster you can get that sucker frozen, the better. Remember, though, that you'll need to do about 48 hours of relaxing in the fridge, first. I tried 24 and it wasn't long enough. 48 was what my birds needed. We did 4 a day so they would fit in the fridge and we ate up all our leftovers and yogurts to make room in there. =)