Over on his blog, Twitch has uploaded a post showing how he mounted two RTL-SDR dongles into a single metal case in order to reduce noise. Twitch used a $2 aluminium metal case that he obtained from a local surplus shop and cut it down to size and added holes for switches and BNC plugs. He then mounted two RTL-SDR dongles in the case and used two MCX -> BNC pigtails to get a case mounted coax connector.
He also removed the USB plugs on the RTL-SDR’s and wired them into a USB B plug mounted to the case, making sure to wind the USB power cables through several turns of ferrite core in order to reduce USB noise. Finally he also added a power switch to the USB connections, to be able to easily power off the units when not in use.