Without heatsinking, my general rule of thumb is to keep power dissipation of TO-220 packages to 1W or less. Find the Rds(on) (i.e., on-resistance) value for your MOSFET's, then compute their power dissipation as P=IIR where I is the maximum current they will carry. For example, your RFP12N10L has an on-resistance of 0.2 ohms (pretty high for a MOSFET, actually), so at 9A it will dissipate 810.2=16.2W of heat. That is not good. I have some MOSFET recommendations here. The NDP6060L, for example, has an on-resistance of 0.025 ohms so will dissipate 810.025=2W which is much more manageable, and should be OK if you add a heat sink.