I think it depends on if you are tractoring them without LGDs...if so or if this is where they will be staying night and day, I'd add a wire floor. Meaties are so dumb that you will run them over anyway when you move the tractor unless you just move it one tractor space over like Salatin. When they are little they will move with, when they are older they may just not move at all and continue to lie down as you try to move your tractor.
Plus you will have the added security of a wire floor in case something wants to dig into your pen.
When I tractored, I just added a small pop door to my tractor that matched up to the pop door on my coop and just backed up the tractor to the coop each morning and again in the evening. Eventually everyone comes outside and into the tractor... and out of the tractor to return to the coop and roost. To encourage egress from the coop in the morning you could throw some BOSS into your tractor and speed things up a little.
