So many seemed to be in need of one, so here's a 3D printable case for your U1. A separate Ethernet version will come soon. 40% fill and 0.6 mm wall thickness should be ok with PLA. There are separate feet if you prefer those, but the case should support the cartridge well enough as is.
The PCB I have is 68 by 100 mm, so if you happen to have another revision of a different size, the case probably won't work for you.
Use 3 mm wood screws for the bottom, 2 mm for the sides. The case can be a bit tight fit at first Ã¢ÂÂ depends on your printer and settings, too.