Boss does not make a seat to fit the 2007 RMK.
The 2007 fuel tank was a one year only design that had a different shape to it than 2008 and later fuel tanks. It used basically the same seat as the 2005/2006 IQ-RMK's but the back of the tank was different.
The 2008 - 2010 Boss seats will fit the Pro RMK but NOT the 2007 (or 2005/06) RMK's.
In talking with Kerry from Boss last season... He did not have the correct information.
I am confident in this answer.