I just saw that. The first time just replying before reading it all the way through first.
They should be fine especially since you'll be letting them out most of the day. I just bought and outdoor thermometer and hung it inside to keep an eye on the inside temps.
I didn't realize it was in texas, I don't think I would keep them in then without alot of precautions. My chickens hate the heat. 90°s are horrible, 40-60° is prefect for us.
I used my horse trailer for a temp coop this spring/summer when I had an evil racoon raiding the coop. It worked out fine. I had the windows slid open all the time, it did get really warm but if you have a stock trailer with slits vs closed windows it would be better. I also had chickens in it...