Two very good ideas, Millet, thank you. My kit comes with two circulator fans, but I agree a ceiling fan would be better for heat distribution. I'd like to do both. I have a lot of vertical space to work with so ceiling fans should fit just fine. And surfactant on the walls is something I'd never thought of.
One thing I'm wondering about now is that the kit is configured so that the front vents and rear vent-fans are mounted about mid-height, which seems inefficient compared to a higher mount. However, because the front vents are relatively huge (3ft across?) there isn't much room to move them up before hitting the roofline. The vent-fans are only ~2ft so I may be able to move them around, but could require moving the supporting frame a bit which will take time that I don't have right now. How important is it that the fans/vents are placed high in the structure vs mid-level?
I'm still not sure what I'm going to do about pollination. I'm leaning towards letting insects come and go, maybe just leaving front doors wide open in the daytime if they can't figure the vent slots out.
One more thing... since I started building I'd completely forgotten that I originally intended to insulate the north wall. However, beause the greenhouse is at a bit of an angle, the north wall *might* be letting a significant amount of morning sun in during the summer months. I doubt its that much, though. Beacuse I dont have extra insulation on hand at the moment I am thinking I will leave it glazed for now and insulate it next winter if it doen't seem to provide meaningful light.
Mark, this kit comes with 6mm dual-layer polycarbonate. I asked if they could do 8mm but was told it won't flex enough at the eaves. It has been somewhat of a pain to install because if a panel isn't installed perfectly straight there is no way to adjust it - it doesn't flex sideways.. I had to shave an inch or two from the sides of some panels as I installed them to prevent overlap. I am starting to see the attraction to polyethylene sheeting.