I got some time to start working this up tonight. This is far from compete but shows a possible configuration of the inner structure that provides linear motion. I haven't gotten around to doing the drives yet and the extruder mount will be reworked... this was just an extruder setup I had laying around so I tossed it in for show. There will be an outer skeleton that the skins attach to. All the electronics will be mounted internally as well as the wiring. Filament spools will be in refillable cartridges that attach to the rear and provide moisture protection. The extruders will use bowden connections. The large opening in the front will have a see-through door. The build platform, I'm thinking, will be a piece of tempered glass with kapton covering and will be removable. Build area is 400x800x400mm (trying to make it as big as possible and still fit on my side desk).
The little clear container on the left side will have wipers on it for cleaning the hotends when filaments are changed during printing.
Looks like the max operating temp for the delrin wheels is about 80 deg C... if this proves to be too low for reliable adhesion (never tried an enclosure before but it's on the low side for ABS in the open) I'll add provision for a heated platform to boost the local temp on the bed a bit.
I don't have the software to check the beam deflection on these 800mm+ lengths ... I'll figure that out at some point... I guess I could calculate it by hand. If anyone knows what to expect with various loads that would be awesome.
-Rick