Recently we started selling modified RTL-SDR units that came with a more sturdy and common SMA antenna connector and a TCXO temperature compensated oscillator. At the moment our dongles are enclosed in a plastic shell. One simple way to improve the performance of an RTL-SDR is to enclose it inside a conductive metal box. This helps prevent out of band interference from strong signals that may enter the device directly and not through the antenna.
At the moment we do not sell any metal enclosures for our SMA unit (but we are working on one). In the mean time one of our customers has been able to modify an enclosure made for the older style dongles with MCX connectors, to be able to fit our new SMA unit. To get the dongle to fit they simply file down the edges of the PCB and drill a new hole in the case to fit the SMA connector.
We note that for good performance with a metal case it is very important that the metal be conductive, and make a good electrical connection to the dongle’s ground. The case purchased was anodized aluminum, which is non-conductive. It is important to file down the coating to ensure a good electrical connection is made otherwise the case will not work.