This sounds interesting. How do you plan to fasten the hwc to the pvc?
As to your question, how long (days? Weeks?) will the chicks be in this coop/ tractor? My concern is how uncomfortable or damaging the hwc will be on their little feet. My other concern is how lightweight this coop will be, and subject to predators flipping it over, which would be disastrous for the chicks if it had no bottom at all. You'd have to secure it to the ground somehow.
So there you have it. Six of one vs half a dozen of the other. I'm not sure what I would do. Actually, yes I am. I'd go with no bottom. But I have a secure back yard with dogs that do sentry duty. They'd be safe in this coop during the day (I'd have to provide shade), and I'd put them in an enclosed, secure shed at night, like a little Rubbermaid storage shed or TuffShed.
Hope you'll post pics of both your build as you go, and the finished project! Good luck and have fun!