I am 5 11 & not exactly slim and have plenty of room. I used the existing floor mounts from the series 3 and bolted the complete Defender rails on top to give an extra inch of height. I may remove or add to height after first long trip. Drivers side is tricky as it has fuel tank stopping me getting access to fit nuts. The big advantage of Defender seats is that the bases lift out to give access to fuel tank and storage compartments