About this 3D model

This is a initial design Im working on for mendel X carraige so I can mount a pair of makerbot Mk5 hot ends. I havent designed the mount plate yet and also havent decided if there would be a lower part or not. One of the recent blogs of a repstrap ( sorry cant find which right now but will re edit this when i do) has the upper carraige with no lower portion. I think as long as were not printing in a varying gravity situation ( i.e. on my boat at sea) it shouldnt matter. NOTE: not parametric and not tested yet.