Just be sure they are not in an area that they will be exposed to water....doors aren't sealed too well, so depending on where they are located within the door it's possible for them to get wet.
Allright cool. Well I won't be installing my set. I don't feel like hassling with it. Someone is charging me $110 to install them and make a cutout for my tweets, get a plate to make it look stock etc..
x2, thats where mine are at. They are safer in the trunk, and much more easily accessible. The only thing is you'll have to run 2 wires on each side up to the front of your car.
I would not put them in doors. Thats a n00b idea because doors are exposed to so much crap. There not even close to being that sealed which is why they have drain holes on the bottom. Not only that, but the shock too, doors opening and closing will take its toll on them.