You don't necessarily need to SEAL the doors, it can't truly be done anyway. The best thing to do is to prevent the back wave from behind the speaker in the door from getting out and the most efficient way to do so is to block/absorb it. It also helps keep the door workings uncovered/modified so it can still be worked on without ruining your deadening. Put the CLD tiles on the door, all you need is 25% coverage on each panel. When I say each I'm referring to the outside/exterior door panel and the inner/interior door panel the plastic hangs on. That will help with unwanted resonances from the sheet metal. The next step would be to build and mount a solid baffle for the speaker to mount to in the door. Mounted directly to the sheet metal, or to that flimsy factory plastic baffle, just isn't the best way to mount the mid. Losses in output, distortions or colorations of midrange frequencies, vibrations and rattles are problems associated with having a flimsy mounting surface. How much effect it has varies from driver to driver and vehicle to vehicle but is and should be a minimum for any installation. The next step would be to obtain and apply CCF (closed cell foam) to the door. Don from SoundDeadenerShowdown prefers applying it to the door with velcro for easy removal and I agree with that myself so the door can be worked on later without tearing up the CCF. CCF cushions all the points where rattles can/will happen. Lastly obtaining and applying MLV (mass loaded vinyl) over the CCF in the same manner with the velcro will complete the deadening and be about the most effective deadening you can do. The MLV absorbs/blocks the back wave, road/vehicle noises, and most all other sounds that aren't the music coming from the speakers inside. Reading up on SoundDeadenerShowdown.com will help you with your research. After performing these steps, if your midbass is still lacking THEN we can help with changing drivers, but as I previously mentioned these should be the minimal steps taken for everyone's speaker installations to help ensure they're getting the most for their money. I have completed all these steps except for the installation of the MLV in my Jimmy. The midbass response from the modest components I have installed in it is fantastic and surprises most everyone who listens to it when I tell and show them there's no sub or any other speaker in the truck making the bass they're hearing and FEELING. Not a bad feat for some 6.5" drivers IMO. Here's some examples. Here's the CLD tiles, right about 25%. Here's my CCF. I stuck it directly to the door since I already had a large amount of RaamAudio's UOI peel n stick CCF on hand. I covered all the holes with it but didn't cover where the window motor is. Here's the baffle I built for my doors. Three layers of 3/4" MDF with a flush mount for the mid. They're bolted to the door with some foam behind them to help decouple the baffle from the door, seal it to the door, and allow wiggle room for getting the angle just right to go through the door card. Here's what it looks like finished. Hope that helps explain and show some of the processes for sound deadening and installation.