The point of using a rack is to let the heat of the oven circulate around the turkey. You don't need a specially designed rack for your roasting pan, but you need something to lift the bird above the bottom of the pan. Balls of aluminum foil work perfectly well; you can also use upside-down ramekins. Also, if the turkey is resting on the bottom of the roasting pan, the skin there will be flabby and moist.
If the skin of your turkey turns out flabby, which can happen when roasting at 325 degrees or less, the situation can be saved: make turkey cracklings while the bird rests. Peel off any parts of the skin that haven't browned well, coarsely chop and put them in a heavy skillet over low heat. The skin will release liquid and then fat, then sizzle in the fat until brown and crisp as bacon. After carving, toss the crunchy brown cracklings over the meat, pass them in a bowl at the table, or stir them into Brussels sprouts.
