I'm thinking about putting an Alpine X 12" sub and a Alpine MRP-F300 amplifier. Would this work and sound good?
Thats not exactly well matched. Type X subs are amazing but very power hungry. I'm powering one 10" type X off a alpine 1000w and it still needs more juice.
300w is type S territory or a much older model type R.
May I suggest looking at the hifonics brutus line mono 1500w or 1800w amps if you want to run a type X. I had one before that was stolen so I replaced it with the 1000w alpine. The hifonics amp performed better on both my 10"type x and my 2 12" type Rs (and are priced very fairly)
If you are stuck using that 300w amp dont run a type X you will be dissapointed.