I can't tell from the picture, but if I'm seeing it correctly, yes I would. When I built my stand for my 120 I used 2 vertical supports on the inside of the squares and 2 vertical supports inbetween the squares for each corner. Granted with an 8 ft span it looks like you have the correct spacing, just need more in my opinion. Might want to also consider a diagonal brace on each 36" end to help reduce flexing, but I'm not sure without being there and working with the frame myself.