How is water going to get inside the space under the window switches? Unless you are a dipstick and make a habit of leaving your windows rolled down during monsoon season, common sense says they'd be snug as a bug in there.

 

You'd be surprised how easily water can get into the doors. Furthermore, the doors are a very harsh environment (always opening, closing, shaking on speed bumps/dips), its very abusive on a mounted crossover. Not worth risking your equipment.

Plus the crossover is just another thing in the door that can vibrate/resonate, decreasing sound quality.

 

I asked the owner of a local install shop about this today when I was in buying a new amp. He looked at me like I was nuts when I asked him about the water issue, and said the only time they mount the crossovers outside of the door is if they are too large to fit properly, or if they are of the $500 dollar variety. Most sub $300 components are built pretty solidly, and don't need to be babied like your first born. The doors in the majority of late model cars are sealed very tightly, so moisture is rarely an issue unless you are dealing with damaged or older vehicles. Maybe your experience is different, but when I opened up the panels on my 05 Scab, it looked pretty clean and dry in there, and I live in Alaska... road salt capital of the Northwest.

Besides, why would vibration be an issue if you were using dynamat or other brands of sound dampeners, which I plan to when I put in my new set of SPR-17c's?

 

Im not saying you cannot mount them in the doors, but why not just do it the right way? No point in risking anything when its easy to put them elsewhere. And I doubt you will want to put sound deadener all over your nice crossovers. $500 or $50, I still would want to provide the best protection and get the best performance from my equipment. I guess I'm just picky about everything, I want perfect sound.

When I used to run passive crossovers, I mounted them to the rear wall behind the seats. There are pics in my gallery.

 

Because running two wires to the back of the cab, and then running four wires back up to the front and through the doors is a ri-goddamn-diculous waste of install time for a pair of $250 components? If you're going to be running new speaker wire from the back anyway, it's not such a big deal as it's simple to put the crossovers between the amp and the speakers, but if you are just running the components off a KTP-445 mini amp placed behind the head unit like I am, it's a bit above and beyond.

Now if I were powering a set of Type X components with a shiny new PDX-5 amp, I'd totally do the install the way you would, as I'd be mounting the amp on the back wall behind the seat anyway, and the giant crossovers that systems requires would fit perfectly next to it.