I fitted the Double Doofer into my Asgard, which is sitting on my patio.
I lifted a slab to dig a 30cm deep hole and filled it with concrete using BlueCircle ExtraRapid Cement. I left it for a few days (not 3 weeks) and then drilled the four holes into the centre of the Asgard floor (painted with anti-rust) then into the concrete.
It’s a belt-and-brace approach, as the Asgard is high security without a ground anchor, but after having my bikes nicked from the garden shed I wanted to maximise my chances.
A 2m Pragmasis chain fits through 3 bikes – you don’t want much slack, it makes it easier to cut if touching the floor.