There are all kinds of engineering concerns to consider, such as design, quality control, systems, process, efficiency, etc. I once worked for a small (under 1000 employees) vinyl window and door manufacturer. We had several degreed engineers, and the AOT is a lot more complicated than a window.
This brings up a question I've had for a while. Would they build in-house or contract out the manufacturing? If they got an order right now for 20 units, how and where would they be built?