[Scénic II] Changing the radio unit.

Hello, this is my first post, and I prefer to use english instead of french because i understand it more easier. I know french too, but I'm too lazy to use it.
So, my Scenic II arrived yesterday. It's has a 2.0 16v engine, Luxe Privilege with leather seating, ESP+ASR, and some other stuff, excepting Xenon and Cabasse.
Questions:
1. The car has a radio CD 4x15W. I went to a dealer to buy a VDO CD Changer ( CHM 604 MP3 ) but I don't know where to mount it. Any suggestions ?
2. He also told me that if I'll change the speaker ( only the ones in the doors ) i will have to cut a part of the support ( i choosed a set of 13 cm speakers, but with a bigger magnet, so they don't fit ). He also told me that, if I choose to cut that support, I will have problems with the isolation. In other word, it will rain in my car. Is that true ? Are there any alternatives ?
I want to mention that was an authorised dealer of VDO Dayton.
Sorry for the long post...

Suggestions:
1. mount it in the trunk, I think this is were most of CD changers are mounted ? Unless this is a DIN1 size Cd changer, in this case you can mount it on the front panel below the radio ?
2. There are some speaker that can fit in your door without damaging the support, this is a very strong recommandation from all users I think . So many people are complaining about water in the doors that you should leave the support untouched. If you decide to cut/remove it anyway, you better find a solution to guarantee waterproof protection for your speaker.
Speakers that fit are Focal slim or Oxygen slimsize also (I use the Oxygen O2 ones, sound great )

Thanks for the great tip with the speakers, I was a little sad about them. The standard ones suck, they are made of pressed paper . The
CD changer is a VDO Dayton CHM 604 MP3, and it doesn't fit in the trunk space, the one on the left. Can it be mounted in the glove compartment ? I understand that I cannot change the tweeters. Is this true ? If it is, it means that the speakers must be without a tweeter, right ? :?