Even though you're cooking at a low temperature, start hot to get a crisp, brown skin. If you're going to go at 250, start off with a 500 degree oven for the first thirty minutes to crisp and brown the skin, then drop the heat to wherever you want to go and finish the bird. I'd definitely use a probe thermometer to make sure you don't go over on the temperature. Also, I've been a huge fan of Alton Brown's "Turkey Triangle" since the first time I tried it.

Here's AB explaining why it works.