I would like to fit a 1200 custom tank to my 2010 Nightster for increased fuel capacity. I have been told by my local dealer that i will also need to purchase a mounting kit @ $222.00 and a 1200 custom seat @ $250.00.

Just wondering if anyone has done this and is the custom seat really needed. There already is a big gap between my seat and the standard tank which i would have thought would accomodate the bigger tank.

Cheers Nomad

Have a look at the parts book diagrams and ask the counter guy to explain why its needed. You can then decide. I have saved a few bucks in doing this. good luck ....beagle.

This has been discussed before on here, do a search in the Sportster section.  From memory I recall, the Nightster doesn't need the custom seat because like you said the gap is already there.  Plus on the Nightster the seat is lower than the bottom of the tank.

Check that you can also use the fuel pump out of your existing tank for the new one.  That would avoid getting stung for an extra fuel pump.