I have done this. :P
It is only a matter of undoing 4 bolts on each seat, and then pulling. Be careful, the spring is under alot of tension. :D
I have put it through an MOT since, and no problems.
As to filling in the gap, one side has been replaced with an LPG tank (vertical torroidal) and I am going to fit batteries and inverter on the other side.
Ed