No lettuce planted yet. Maybe some transplants could go under plastic but I don't usually do that. Lettuce transplants are handy, tho', right thru the growing season.
GWR, it looks like the roof may overhang your windows. My South Window is in a gable wall so the overhang is way above it.
I can put 4 boxes on the window sill and 4 on the table. Those will get a long period of sunshine. The next row will get quite a lot less sun. The seedlings just starting out can stay there a couple of days. Then, they had better move forward into better light.
The weather service has just changed our forecast. Only 2 more days of sunshine. Shoot.
Steve