I did this for a while in my GQ wagon, then ripped it out. I have a SS watertank behind the middle seats, plus a cargo barrier. What I found was the removal of the seats only gave me a height advantage of having the seats in place of about 125mm from memory. I had a flat ply floor on a 25mm rhs frame, and really found the area was not any more useful with the tank in the way. maybe you are looking to open the entire rear of the vehicle from back of front seats to rear doors? I hate to be the scare monger, but the old RTA will nail you for seat removal as well especially if the seat belts are left in place. The 'nightmare' VASS' engineer i consulted wanted to legally turn my 7 seater into a 2 seater because of hardware on the cargo barrier - ended up not using him and mine is now a registered 5 seater. Food for thought.