Sea&Sea has announced some time ago their new housing for the Canon EOS 400D. Meanwhile, Wetpixel member Pakman has found a way to use the Canon 400D in the DX350D housing without any major changes. Indeed, only the buttons on the left of the LCD are in the different place than in the 350D. The solution is the use of wall anchors (specifically, wall anchors nylon size #4 worked great for me) in the place of the rubber buttons originally in place.
This solution is great because the housing can be retrofit to the 350D anytime, just changing the wall anchors for the original rubber buttons.
Also you can see completely the new 2.5 LCD in the housing. This nice bright LCD shows you all the camera settings without needing to put your eye on the viewfinder or on the old display.