We got to the greenhouse having read all the vent-fitting instructions really carefully... only to find there were extra instructions that said we needed to put the vent openers in the fridge before fitting.
So fitting will have to happen tomorrow, since right now:
On the plus side, that left us time to dig a moat!
The greenhouse is at the lower side of the allotment, so it will tend to get puddles on the floor unless it's got good drainage. This is the first section of the French drain which will take water away from the greenhouse base and take it to the stream which runs along the southern edge of our plot. The trench will be filled with a perforated pipe and gravel, then most of it will be covered with slabs - so that people walking over it don't fill all the gravel gaps with mud, as that would reduce the drainage.
But it's more interesting having a moat than a boring old drain...