Attaining some good mid-bass is more about the install than drivers, unless we are talking Roadmaster vs. Scan-Speak or something lol.
Sealing up that door will make the biggest difference, but I assume those inner door skins are very open with lots of holes/access gaps and whatnot.
That's quite a bit of power, it will be tough finding drivers that will take and use that power well, I can't think of many 5x7" speakers that have high power handling. You might as well keep that amplifier turned down, and essentially use checking for bottoming out and sounding muddy when turned up etc. to set the gain and crossovers.
Making or buying speaker adapters is not a bad idea, as it will make for more mounting depth, and be a baffle in itself. And there would be a ton more options on a good 5.25" and better yet a 6.5" set. I recommend staying away from ever using MDF in or on doors, MANY cars allow plenty of moisture on the inside of the doors, hence, the reason many manufacturers use vapor barriers. Wood, in or on most car doors is not a good idea as a whole starting with longevity's sake; it would certainly cause swelling and flaking away of the MDF eventually. I've seen it happen a hundred times. On a Windstar, well, unfortunately I can bet moisture is abundant after a rain fall. There are many vehicles out there which are probably going to be fine, like my newer Mercedes C and S-class are sealed up incredibly well (interestingly enough, being SEALED is actually part of the vehicle's safety and airbag system, but anyhow)... Of course, water can still easily head down the window glass on the outside as weatherstripping is soaked and wear away and whatnot. So, sure, the inner door skin is sealed away, but the area between the door skins can have moisture sitting in there, which means the speaker's motor and the inner side of the baffle or mounting ring will be subject to it from the inside. I highly recommend utilizing some "plastic" cutting boards, and making the adapters or baffles out of that. They work phenomenally, and if you need more mounting depth just do as many layers adhered or cemented together as you need for thickness, but I guarantee a simple Google search will find you a place that makes adapters for that vehicle.