I wouldn't do chicken wire, maybe a 1''x2'' hardware cloth though. depending on where the tractor will be you might not want a bottom at all. if it is going to be on uneven ground i would go with a floor
Are you thinking layers or meat birds? And how many? I’m running a modified version of a Suscovich design for layers, with a small enclosed roosting box with a 1” hardware cloth floor so most of the poop falls through at night. I used pneumatic wheels as we get quite muddy and I have some rough ground. I’ve found them to be quite adequate for my needs. I get better (more even) fertilization of the pasture from my meat tractors though, which are sort of Salatin styled.
I found it safest to have a flexible wire apron than could be weighed down with a few rocks... if the coop is sitting in a not fully flat spot.
Make it strong enoug for a dog to bag and jump against it.
Also, you need quality wire, securely attached with tiny holes...the problem with a tractor is they can't run away.... so if predators can reach in... they don't have a chance... even if they are awake.
I kept the bottom of my tractors open.. no wire.. but I don't have any digging predators except for dogs. The quality wire is for the sides and roof.
Do you have a 4-wheeler? Makes it easy to move even a huge and hefty tractor.