12 Volt, the Xplode series has a bad reputation for not holding up in many cases (obviously not all or they wouldn't be liked by anyone), but they tend to blow a bit easier than other brands.

For the speakers, what size holes do you have? And do they need to be shallow mount?
Infinity Reference's are very good speakers to work with subs due to their superior mids and highs.

As for the sub, one possiblity is this http://www.crutchfield.com/App/Produ...10P&tp=114
It should fit perfectly behind your rear seating if you have a back bench.

But what kind of seating setup do you have (I am not extremely familiar with the setups of Rams interior [&o])

 

i have the fold up and down full back seat bench

 

there are a few companies on the internet that make custom boxes for your truck. I am in the process of getting a dual 10" downfire box that will fit under the back seat. The only problem is in a 10 you only have about 5" of mounting depth so most speakers won't fit unless they are shallow mounts. I like the kicker's with at least a 500W amp. The 10" sub will keep up with quick bass from rock music but wont hit quite as hard as an 12 will. one place to look is millionbuy.com or onlinesteros.com They have very reasonable prices and carry a lot of good equipment.