I guess it really depends upon your comfort level. I did line the entire bottom of my run with hardware wire that I screwed onto the frame. It was actuallyuch easier to line the entire bottom than to bury an "apron" of wire around the perimeter. My run is about 16'
x 7', somewhat smaller than yours. My birds have access to their run 24/7; I don't worry about preditors, and we have plenty! Good luck with your project... I'm in the process of designing our next coop, about 24' x 12' and haven't yet decided on the new run. I wish a new coop/run would just appear!