Usually an extended cab does not have four doors but now they do. At first they had about 18" behind the seat for stuff then more seating was added, two jump seats facing each other. Then it was extended a little more and a very small second bench seat was added. Then a door that opened from the rear of the front door was added on the passenger side. Then it was extended a little more and a door was added on the drivers side making a four door where the front doors had to be opened to allow the rear doors to open. A crew cab is just a four door truck. Ford, Chevy, GMC, Toyoty and all the rest have their own names for the various versions but I hope you get the idea. Club Cab is Ford's name for Crew Cab.