Most turkeys don't go inside at night like chickens. Not willingly anyway. They prefer to be out and to roost as high as they can possible get. If the roost you install under your deck is as high as they can possibly get, you've got a good chance of it. If not, I wouldn't hold your breath. And keeping them in for weeks, even months doesn't work either, ime. They'll return to that roost spot for a couple days. Maybe a week. Until they get up the guts to try a different one.
The nice thing about turkeys is that they do tend to street smart about it. As someone else said, they choose nice high roosting spots and they put themselves to bed earlier than the chickens which reduces the chance of an attack at dusk.