Built specifically for the Nighthawk frame and the Boscam TS351 but will likely fit lots of other transmitters. I put grippy shelf liner under the transmitter and a zip tie to on to hold it together.
Inner dimensions of the tray are 27.2mm X 40.5mm X 7mm
The centers for the two bolt holes are 43mm apart.
I also made a smaller version for the TS5823 Here: http://www.thingiverse.com/thing:826152