deadener is less important than recreating all of the factory seals. you will notice that the factory speaker, while cheap, has foam seals on both sides of the basket. one seal is obvious, seal to the metal and use something soft and thick to prevent rattles. the second one is neglected and vital to success - the seal between the front of the woofer to the door panel/grill. if you do one thing, it should be weatherstripping foam around front and rear to seal to the door and the door panel.
beyond that, some deadener will help with resonance.
some bags of fiberglass in the door cavity will help with midrange clarity by absorbing sound inside the door (like putting fill inside a speaker box).
beyond that, sealing the door holes will take a step to give you more midbass response.
regardless if you have a sub, your speakers are what provide bass definition by supporting the bass line harmonics that we hear. if you want music that sounds good, the front speakers are the most important part and should have the most time spent.