What are you doing about cooling inside the box? My first CNC machine was built into a closed box but it got far too hot inside. I burnt out the motor of my Makita C700 router by installing it in a temporary installation with insufficient cooling air circulation so can say from experience that this matters. I'd also be concerned about the build up of chips and the consequent fire risk if you have no dust extractor in there. I had some experience of that as well, it was why I finally decided to dissmantle the box.

I've just switched from using a brushed router (a Chinese clone of the same C700) to a 2.2kW water cooled brushless spindle on my CNC router and the drop in noise is amazing. Now it's the dust extractor that makes the most noise and there is no high pitched scream which could be heard for some distance outside my shed.

Kit