This is a HOME Audio forum. You need to search for a CAR Audio forum.
While a Car audio forum can be more helpful, I don't think anything he asked isn't something we can't answer. It would have been better if OP asked in the DIY subwoofers forum, though, as car audio subs are sold as drivers, not finished products.
The Alpine MRP-M1000. Googling this we see it gives
600 watts into 4 ohms @ 1% THD
1000 watts into 2 ohms @ ??? THD
Just
guessing, but into 8 ohms that probably means you're gonna get around 300+ wrms. I'd prefer to do an amplifier power rating at .05% THD or so, which would probably knock that down to ~270 wrms or so. Plenty of power.
Now onto the driver. Wiring the two 4 ohm voice coils of the RE Audio SEX12D4 into series, we get an 8 ohm load which will probably give you the best control over the driver. The driver can thermally handle up to 600 watts rms so you're fine here too. It seems like a quality driver.
Now regarding an enclosure, that depends on many, many factors. As a general rule, car subs can sound better with a higher Q like .8 or .9 because of cabin gain in lower frequencies. Personally I believe you should always give your EQ the chance to compensate for cabin gain, and give your driver plenty of room to work with but that's just opinion and not everyone has a worthwhile DSP, although you might get good results with something like the Alpine Imprint. If I were doing audio in my car and had the money, I'd have a lower q and have a JBL MS-8 EQ it out flat, as well as control an active 2 or 3 way front stage.
Anyways regarding a box, I can't model it properly as I'm on a public computer right now but based on what I'm seeing on the T/S parameters, I'd guess anywhere from 1 to 2 cu ft internal enclosure volume in a sealed box would work decently. You can try modeling it in win ISD but realize that doesn't factor in the cabin gain found in a car. Just shoot for a qtc around .7 to .9 I guess.
I probably wouldn't bother with a vented box in a car. Although that driver can probably work in a vented box, I consider vented boxes to be for wider spaces with less low end gain.
Alternatively, I recommend the
Exodus Audio Shiva X2. not only is it an excellent driver, but there's excellent
application notes for it including a box design for a car application.
Wiring that sub in series would give you a 4 ohm load, so you could pour 600 watts into it.
