
revaar |

Invulnerable Rager +1. Add in an Unbreakable Fighter dip, to expedite picking up Stalwart and Improved Stalwart. This will get you to 19/- at level 20. Forgoing the Unbreakable dip gets you 20/-, but costs a couple feats more. Animal Totem will give you +6 Nat. Armor at level 20, if you are a Tiefling, you can pick up Armor of the Pit, getting you 2 more, for +8, and an amulet of Natural Armor +5 gets you up to +13.
That seems like a good start to me.