For freestanding cages, I just bent the hardware cloth over the edge of a board or work bench to form the corners and used J-clips for the connections and hinges. I made a 3' x 5' brooder 2' tall with a top opening and a side door, using no wood. It held its shape very well although the top opening could use a little reinforcement. I have treated it pretty rough moving it around.
For a tractor, I'd be surprised if it needs any real stretching. I envision you building a frame with wood and then covering that with the hardware cloth. I'm pretty sure you will get it tight enough just fitting it and attaching it. I covered my window and the vents to the coop that way and it was no problem at all.
To attach it, I cut a piece of 2x4 so it was 1/2" thick and made a sandwich with the hardware cloth. I used a very few staples to hold it into position on the frame around the windows or vents, then screwed the 1/2" piece of wood over it. I find this makes the connection a whole lot stronger than just using staples.
Now chain link or welded wire can be different as far as needing to be stretched.