If you are using a military surplus patrol bag, you are going to be soooooooo cold in those temps. I used one in the mid 20's but had a fire going all night long. If I didn't have that fire going, I would not have slept that night. 30 degrees is pretty wrong, it's more like 45 for most people.
If you are going to be wearing lots of clothing, you need be sure that you don't end up fitting too tightly into your bag. You will end up pushing up against and compressing the insulation in your bag and the tightness of your bag could compress any of your down or fluffy synthetic clothing. If that becomes an issue, you may need to unzip it and use it like a quilt to keep the effectiveness of all your insulation.