Responded to @zrail:
@zrail That’s lower than I expected. I have my UPS draw additional 15W on top of the 30W from NAS https://kaspars.net/blog/powerwalker-vi-500-r1u
A 10W source in a 20x20x20in box gives you 6.6W per m2 or 0.33W/m2 at dT=20K which is achievable with 4in of pretty much any insulation board.