We have been getting a lot of inquiries for a single side EXR Fuel Tank that will add roughly 4.5 gallons of extra gas to your X3. But we don't know what side to build it for. The tank will be the exact same shape and could go on either but the filler neck should be by the door for easy fill up. The few X3s I have built had SSV subs under the passenger seat. We want to know if you guys have a different set up. What seat is your sub under so we can build the tank accordingly.