There is this rack panel which allows you to mount 8 micro converters side, with external access to the SDI ports:
https://www.markertek.com/product/ctx-b ... convertersI suppose you could use two of them if you need to mount more than 8. If you want to mount them entirely internally, then a rack shelf of some sort would probably work. You can probably remove the screws from one side of the Micro Converter case and mount the converter on its side, screwing in from the bottom of the rack shelf to secure them.
I probably wouldn't worry too much about heat with the Micro Converters as those units don't seem to get very hot. The larger Mini Converters (especially the 4K Mini Converter models), seem to run much hotter and are probably using the metal case for heat dissipation. But I don't think the same thing is true of the Micro Converters.