This youtube video shows exactly what you are all trying to do:
I've been working on a similar project for a while, just haven't had the time to finish it. I used this dummy camera which is waterproof (still seal it up with silicon!):
http://www.amazon.co.uk/Friedland-Respo ... B002PK0UU8
I used perspex in mine with adhesive nylon for the pi to sit on. The camera fits perfectly where the dummy one is and you just use nylon bolts to fit it to the existing plate.
It works great, however now that I've seen that youtube video I'm going to add my PIR to it which is what I've been trying to work out how to do but that video has solved that!!
This is the best camera solution I have found. I've seen lots of IP Cameras, but for the price and the amount of this you can do with this since it's based on linux makes it so much better. For 80 quid you can make a camera that works better than the ones in the 100's with full 1080P HD, IR and PIR!