I own a quadcab dodge ram, but I do not have a system in it. I own a chrysler 300 and I have a wild system in it. I've contemplated a system for the dodge ram and here's what i came up with:
On ebay you can buy a box for your truck to hold up to 10" subs. You will run into various problems with space in this truck, as the box will need to go under the rear seat and there simply is not much space. I bought one of the boxes I mentioned for 2 10" subs. When I got the box, I realized the dimensions for the subs that can actually fit are really small, limiting the type of speakers you can use in it. Also, the box barely fits even though it has so little air space.
My conclusion is that you will definitely need a custom built box for the truck and you may not be able to go with anything more than 2 mediocre 10" subs. I say mediocre because any 10" sub thats worth a damn is going to have a mounting depth that is simply too much for the spacing in the truck.
This still doesn't touch on amplifier placement, and you will either need 2 amplifiers or 1 5channel or 6channel amplifier. 2 amps will take up space, while any D-class 5channel or better amp will take up space.
As you can see the options are really limited unless you want to spend some money having some options completely customized for you.
As far as mids and highs, the spots in the doors can hold anything you want to purchase up to 6.5" or 6x9. I have 6.5" component sets in my 300 and I love the sound. I have Mb quarts. What you choose for mids and highs will just be based on your preference and your wallet. You will need an aftermarket amp for the mids and high, especially if you go with subs.
Headunits, you will be limited only by the DIN size of your current headunit. Mine was a 1.5DIN so I was mostly limited to single DIN units.
