Hi swannRE, and welcome to the SOS Forums!
I’ve still got a Boss SE-70 half-rack processor bolted into my rack, and all you need
is a ‘1u rack shelf’, which typically costs somewhere between £15 and £25
Here’s one for example: www.soundsliveshop.com/p/1U_Rack_Shelf/AHALL-8754
simply need to drill a single hole each to mount your Micro Rack series units.
One thing to watch out for though - many cheap rack trays are quite deep, making it
difficult to reach the input and output sockets on the rear panels of typical half-rack
width FX units, and since they are made from 1.5mm steel they can be a pig to trim to size
(as well as producing lots of sparks when you try