Yardfulla poopers
Crowing
This is what we did when we had city chickens, we built a run extension that could be detached during the coop move and reattached at new location. I wish i had pictures of it 

If you are set on a tractor, could you make additions of the run style for the tractor that you can connect to the current run? Or even a permanent run/coop?
Maybe a larger run that the tractor coop can be moved into so that you still have the freedom to move the tractor if you choose to.
You may be able to look on Facebook or Craigslist for possible supplies or things that are free, if the cost is an issue.
I do think you would like a larger run and the flock would be happier plus less stress on you.