I wanted a proper enclosure for the KiwiSDR, so I ordered a Hammond box on eBay (model 1590J, 145x95x49 mm) and got it reasonably cheap from the UK. It is in fact a snug fit! I suppose though, it needs ventilation, so how about drilling 9 holes in a square on the top and the bottom where the device is warmest? And add rubber feet to the Hammond box so air can circulate.
As for fastening the Kiwi to the box, there are two alternatives. I have already clued silicone feet to the device's metal frames, so option 1 is to just use a clue gun on the Hammond and fasten the silicone feet to the box. The other option is to fasten the Kiwi to the box with machine screws from the metal frames.