I've tried row covers and since my garden does not receive full sun all day, I think it was a little too shady for robust growth you expect from brassicas. I did come up with a good support system for my row covers. Here election posters are supposed to be removed the day after election, so I help. The metal frame for the posters are excellent for holding row covers as well as making little plant fences to tidy wayward or floppy plants. For row covers just place them 2-3' apart, loop some string along the corners and stake like a tent at the ends. Place the cloth over them a weight with narrow boards on either side, continuing the cloth to the end stake.