I think, in normal summers, plastic greenhouses are fine. I wouldn't go to,the,inconvenience of insulating your greenhouse unless you,want to for the winter. To help ripening, I remove leaves.....took every leaf off 4 weeks ago because I had a touch of blight and every tomato has ripened. Is it bananas or apples that,help ripening process maid? Some put tomatoes in a dark drawer, don't they? Victor, did you plant them early enough? Did you pinch them out to restrict the number of trusses? You say you have a 5' fence...is greenhouse in full sun?