Actually, he made his own from scratch, but having chatted to him we came to the plan I detailed above.
Best thing is to try and find a net like the ones we have spoken about, and then then sew it to a ground sheet of the size you require.
I mentioned using the actual GoLite bath tub floor as the attachment point are in the right place.
It is a shame that no one has seen the gap in the market and made a nest that is not for size for a massively popular shelter.