Only the swivel base. You unbolt the seat from its base and insert the swivel base by bolting to seat base and seat. It raises the seat less than an inch and offsets it slightly to center of vehicle (inch or so) to allow for swivel. The lever to activate the swivel sticks out between the legs of the passenger. I trimmed its length because I thought it stuck out too far and added a plastic cap to end of trimmed rod. Took less than 1/2 hour. It was helpful to have a second person to help hold seat while bolting to swivel.
It can be swiveled with door closed by turning and sliding seat forward or back in several moves, but works much better and easier with door open. Turn seat back toward middle of vehicle. It locks in place only in the driving position. When swiveled it can be turned at any desired position.
2012 Forest River Sunseeker 2300 Chevy