The m101 chassis has a #10-32 threaded insert mounting hole on the bottom towards the back. Two m101s can be mounted side by side in a standard 1U rack tray. Use a #10-32 x 1/2” or a #10-32 x 3/8” machine screw. Do not use a screw longer than 1/2”.
Grace Design does not supply rack trays, but they are pretty easy to find -
http://www.middleatlantic.com/rackac/storage/shelves3.htm#3
http://www.raxxess.com/catalog.asp?CATID=117