I would consider adding a pair of float and setting them pointing to the rear to A) offset the nose up attitude of the housing when using a dome port and B) lighten up the overall weight of the rig. To me, it makes more sense than to add extra weight and it is the way my kit is set up, for macro I move the float forward to offset the nose heavy tendency of the macro port and I can adjust the trim independently no matter where my strobes are positioned.
The camera will need to be pulled back to remove the battery, no choice, otherwise the split in the housing would need to be way too much up front and would compromise the layout of the controls. It is good t remember that this is a still camera with video capabilities, something that seem to be forgotten often when discussing the 5D Mk II, the idea is to have the best of both world when possible, but if a choice has to be made, and believe me it happens, then the still camera outweigh the video camera. it would be totally different if we where designing a video housing for a video camera with really good still capabilities, then you would have the usual battery in the rear of the camera and not have to deal with SLR optical viewing path, lens interchangeability and what not. That is what I mean by it being first and foremost a still camera with video mode.
A lot of thought and consideration went into designing the video access features, all this while trying to keep the rest of the natural controls encountered on a modern DSLR accessible and as uncluttered as possible. In the case of hybrids such as this one, one has to consider the initial philosophy and purpose behind the camera design and intention when designing and manufacturing a housing for it.