I was in Van Bodies (Lancs) Ltd in Morecambe a while back and they had a few electric vans in for conversions (Campers and kombis) he said they Bond a floor with rails inon the bare floor with a system from Germany, which you then attach the seats too. He was suggesting that's going to be the way forward now with electric vans etc
It looked super clean and tidy, there is something in my head that feels nervous about a glued in floor but its fully tested.