Simply not enough volume for a proper 12 enclosure.
It's hard to define pretty loud, but it will sound much better than the 12 or other configurations.
The SA8's use a 2" voice coil so if you want to be louder and be able to throw more power I'd suggest looking into a 2.5" voice coil sub.
With that being said I've ran two SA8's on a Sundown 1500 @ 1 before and they handled it well.
I'm on Titan Talk as well. I've done a number of designs and boxes for people over there (on facebook page mainly but sometimes on the forum)
Tech12Volt also makes a nice box for 8's as well for our trucks if you want one already done.