This Amp correct for these subs?
 

So I own a 08 F-150 Supercrew and decided I would like to add some subwoofers. Ive never owned a car with aftermarket subwoofers so I decided to do research before heading to the audio store.

I went and after speaking about the set up using shallow mount subs installed underneath the rear seats the speakers he suggested were these.

2 - Pioneer TS-SW301 (TSSW301) 12" Single 4 ohm Shallow-Mount Sub - at $72 ea.

The amp was this

1 - Rockford Fosgate R250-1D (R250-1D) Class D Marine PRIME Amplifier
- at $98.

My question is if this Amp is a correct amp/has enough power for these two speakers?

From what I've read and understood two 250W RMS subs would need a 500W RMS amp at given load. So with two 4 ohm SVC subs they would have a 2 ohm load and need 500RMS amp where as the rockford the audip shop suggested only has 250W RMS.

Is there something wrong with this picture or just me? I've tried to provide as much relevant information as possible so if I missed anything let me know.

It is not compulsory for you to have 500watts rms but optimum performance will be achieved with an amp that is rated at 500-600watts rms (I would use a 600watt amp since most power ratings on amps are based on 14.4v and vehicles with stock electrical usually float between 12-13v). The amp is question will still provide decent output and your overall bass response will be improved if tuned correctly.

Also, there are many other products out there that will perform better and be as cost effective(maybe a few more dollars) as the items you are considering but if you've listened to those subs on that amp and like it then go for it.

RE Audio's entry level subwoofers (RFX/SRX) have a good price/performance ratio (available on sonic electronix $50-$100 each)
as well as my choice:
Sundown Audio's E series (available at selective sounds in Ontario $75-$125)
NEW Sundown E8v3 on pre order for $75 - 8"woofer that will perform better than the Pioneer with the right power and enclosure (a friend has 2 of the older E8v2's and sounds louder and better than my old 12" JL w0's)

If you're happy with those subs, then I'd suggest the Kenwood KAC-8105D amplifier.
It'll do 500W into a 2ohm load. I am currently running this Kenwood amp, at 4ohm for 300W, to power a Cadence 8" sub in a sealed box. Plenty of bass for me.
I'd highly suggest the Cadence subs that I bought. They are $47 at Online Car Stereo's site.
Kenwood KAC-8105D (kac8105d) 1000W Class D Monoblock Car Amplifier

Keep in mind that shallow mount subs are usually (this is a very big generalization) used in MUCH too small enclosures. I would recommend a slightly larger amplifier but you definitely dont have to go crazy.