I know one guy here in Sweden that put a port in his midbass box.
Before I tell You what his conslusion of this was, I need to tell You that the box was incorprotaed into his dashboard, with the port and speaker facing up and into the windshield.
He eventually sealed the boxes...!!!
The ports made so much noise that it was annoying and it also affected the sound...
This doesn´t mean that it want work for You, but I would make a testbox and listen to it before I make it "final" so to speak...
In theory, the extension of the lower frequencies from the ported midbass will increase the ability for the midbass to transition into the bass region. The lower in frequency I play my subs, I believe, the better the up front bass imaging will be. I understand the problems with vent noise but it has been my experience with subs that a properly designed vented enclosure has little to no port noise. How well this will work in the higher frequencies I have no idea. I just wonder if the direction of the driver not the direction of the port will dictate imaging or is it a combination of the two.
There was a guy who stuffed 52 (yes 52) 6" drivers in a snailshell-bandpass configuration (sorta like how BLOSE does their designs) and it did something like 150+dbs. So there is a advantage to doing it, just needs to match your actual needs or desire to do so.
As an addition to what's already been said, here's my thoughts;
Some of the problems you'd encounter would be:
-Controlling the resonance damping through a combination of box size and driver selection
-Tuning the box to meet the response characteristics you want (especially since most of us who would use a ported box wouldn't have very much room)
-Step response, due to size restriction
-Phase variations of port response vs front speaker wave
-Port noise, like you guys said
-Stop band attenuation
Some of the benefits:
-Higher SPL over a small band around tuning
-Stop band attenuation, (yea good and bad as per application)
-Having the ability to tune the box. (same, good and bad)
i wouldn't do it for a couple reasons, the first being that it would be a b**ch to incorporate into a door. You could do it, i've thought about it and planned it, but it wouldn't be easy. Second, from the fr graphs i have seen for ported enclosures, it seems like there is a boost centered around a small band of frequencies. This is great for subs cause they play a limmited number of frqs, but I want my midbass to be as smooth as possible. IMO, for a car, it would be much better to put the midbass in a larger sealed enlosure. That way you wouldn't have a big boost in only one freq. but give you decent lowend extension, and be a lot louder than IB.