I just bought the swivel for the passenger seat from the Sprinter Store. Put it in last weekend. Very easy to do, and no, you don't have to fireplace the seats. This just goes on the base. We decided to just do the passenger seat. It does raise the seat a tad, and you have to remember to raise the seat before you swivel!
Lynn & Dan Hochradel, & fur kid Carl
2015 Entegra Anthem 44B, Dodge Ram 1500 Quad Cab