I wasn't keen on cutting into my doors as well but when I went to a local stereo install shop to get a price on them to install my system, they said that the doors would be the best location since it offered a "perfect" dead air space to enhance the bass.
In the end, I installed the system myself including six inch Pioneers in the doors. Surprisingly, the sound it awesome and I won't need to add a second pair of speakers behind the bench seat as I originally planned.
If you check out my pics you'll see the placement of my speakers.
Good Luck!