I am absolutely thrilled that you are happy with this method. I currently have 15 happy, healthy chicks living outside and I am so relieved not to have to worry about them with a heat lamp. My heating pad is now turned down to 3, but they are only in the cave at night, when temps are still in the 30s. The rest of the time they're eating, exploring, scratching and learning how to be chickens from watching the Bigs all around them.
I meant to post this yesterday, but forgot. Now seems as good a time as any. The one surprise to come from this was the Littles' confidence! Last year's chicks, were brooded the "traditional" way, with a constant heat lamp on them, me fussing over them all of the time, and them not having a secure, dark place to hide if they got spooked. I'm sure those of you who are not new to chicks have seen the frantic running full tilt all over the brooder looking for a place to hide if you suddenly enter the room they're in. By contrast, the Littles look up at me when I go into the run, then most go right back to whatever they were doing. If I enter their pen, a few will hightail it into the cave but they usually watch me from under the awning, then pop right back out when they realize I'm no threat. As I go about filling the feeder and checking water, almost without exception they'll be wandering all around me, and they're so calm!
It will be interesting to keep track batch by batch, and compare notes with those of you doing this, to see if this is a fluke or if this steady confidence comes from the security they feel in the cave.