I'd look into a Lambda PB10 or PB12 from www.lambdacoustics.com for some great bass (deep and accurate, these subs are not SPL monsters).

BTW, go for a 4ohm SVC (single voice coil) sub. You'll bridge the rear channels of your RF 200.4 which will give it 100w RMS (pleanty for a PB).

1999 Ford Contour SVT #900/2760 (SOLD) 2005 Mazda 6s 2003.5 Mazdaspeed Protege 1998 Ford Ranger 4x4