There is a scientist named Crockett in one of the rooms in the Hubologists' San Francisco base (who, incidentally, is not an adherent of Hubology) that can improve Power Armor into Hardened Power Armor. He can upgrade it for a fee of $10,000 (which can be immediately stolen back) or can be threatened into doing it with a high Speech skill. Alternatively, you can negotiate to have fuel transferred from the Steel Palace to the USS Quetzel in exchange for his services. However, he can only harden two Power Armors.
If you've completed the quest to kill the AHS-9, you may not be able to get the needed dialogue to get this hardening process done on the armor.