How do you "train" older outdoor cats to be comfortable around people (when the cats are in a new environment)

We want to take 2 outdoor cats from one location (a public dumpster area) to another (our backyard), but want the transition to be easy on them. We'll have food, water and a cathouse for them, but want to be sure they won't run away and/or be fearful of our presence and their surroundings, etc. How do we make them comfy?