My dad and brother built an outdoor low tunnel using 1/2" pipe and the same heavy weight spunbonded row cover I used during the germination trials. They bent the pipe around a big tree in the yard a held the row cover down with rocks.
Since I had 144 plants I've been giving away lettuce, mizuna and spinach seedlings to anyone that can plant them. They were planting a few weeks ago before the spring heat wave. My dad says they grew like crazy last week and they have been eating fresh salad everyday.