Structural engineering.

Today has been a biggie, in the rain.
Got up late, dry but cloudy. Went out with the dog and saw Albert on site with his brother. Went and had a chat to explain where his nettles had gone, seemed a bit vague, more worried about the rainwater on the adjacent path than vandals. Still able to give him the shed key he had left in the door. While we talked the heavens opened.
Went back home and in a lull covered the greenhouse frame with plastic sheeting and an old gazebo cover, this kept the inside "dry" and I was able to set to work attaching the frame to the sleeper base. First up I measured, cut and screwed to the sleepers the 2"x1" treated timber to take the lip on the frame base.
Fortunately the extension, that I have not used, had two bits of 3/16" x 1&1/4" flat aluminium bar that lay over the joint between the frames. I have used one of these to manfufacture angle brackets attached to the frame using, the bolt slot in the bars and the correct aluminum bolts, and brass screws into the sleepers. Six of those and a number of strategically placed brass screws straight through the base bar into the sleepers.
Only got wet once, when a plastic sheet grew a puddle inside the frame, then slipped in through the frame to decant the puddle on my lap as I sat beneath.