Ok guys, here is the preliminary model for the suggested chassis plate.
This should be compatible with all Carbon versions of the E4 and will likely include a redesigned top plate to go with it.
This model is based on 2.5mm carbon plate. When I get around to prototyping it, I will start with 2mm stock to verify if the new design will be stiff enough at that thickness. Besides, it's what I have on hand.
In case you were wondering, the battery may be removed by pulling off the side belt and middle brace. I may design a new middle brace to make installing and removing the battery easier but I suppose I'll cross that bridge when I get to it. In these days of lipo batteries I find it rare that I will remove my pack. I just charge and go. Either way, it cant be worse than taping packs in every heat when running NiMh.