Yes, seat remains underneath :)
Have been running this setup now for 2 years and all good - just gonna add a Drifta draw to the top of it now and move the ORS slide and fridge on top...
Printable View
....and to add to roamer's query - just two (RHS in photo) of the 4 factory tie down points are used to hold it all in place?
Yes just the two tie down points on that side of the car.
In answer to the other question about the ORS fastening....
There is approx 12 screws that go into 24mm of ply as on top of the base board there is another 12mm piece of ply which is a bit bigger than the slide footprint. Therefore the screws go through more than 12mm of ply also :)