A LOT of information here. Breakdown below from John and the customer:

Let's assume we start with an E-41L1.
Internal Dimensions: Approximately WxDxH 840mm x 800mm x 500mm. Ideally external dimensions would primarily add height or depth rather than width.
The box will likely need to be shortened.
The box will have a front full opening door.
The back will need to have a small cutout (centered left to right but height to be determined) measuring 150mm x 200mm
                The cutout will be left open.
                The customer will add a door to cover this opening once they receive it.
                This door will be used for a device to go into the chamber.
                As such I feel we need to address the air flow.  
                Can we divert air around the door opening and still have good uniformity?
                                The rear wall plenum would need to be modified.

                OR

                Could we offer side to side air flow as we see in some stability chambers?
                This is a good question for the engineers to make a recommendation
Temperature Range of 4C and 50C
Additive and subtractive humidity but usually maintaining 80%RH
Initially at least they are looking at SW but I can see a push for SB.
                800 µmoles/m2/s
Additive CO2 up to 5%
HEPA filtration inside the chamber.  Not worried about what leaves the chamber.
They are also working with another incubator company.  That company doesn’t have exactly what they are looking for although they are working to create something.   
The chamber will need to house Bioshakes by Q Instruments so we’ll need electrical receptacles.
This may only be a one and done but there is potential for more in the future.
                As such they would like to know if there is a break down for engineering fees for the initial chamber.
                Then, what is the estimate for the chamber.
                I believe the expectation is that they would not pay for engineering fees again if they buy additional chambers.

All in all this is not that complicated of a chamber.  Primarily we need to shrink the height of the box and deal with the rear wall plenum.  Everything else is pretty standard. 
