Ranger - "Higher Vampire" [5th Campaign, 5th Mission]

Can you supply troops using secondary heroes? I'm just used to completing all maps quickly. The difficulty is set to easy. After the first week, I captured the garrison and the orange. The only thing I want to know is: how can I clear the garrison without any overall slowdown and without losses???
And the version is 1.6. I don't understand why there are so few skeletons...