I've recently switched over to using a homemade sidemount rig for diving. Finding no good source for the necessary backplates (or some CAD files allowing me to have some locally cut) I decided to produce my own in OpenSCAD. Initially I was planning to simply mock the plates up in ABS and then have them cut out of stainless steel, but at the current 5mm thickness printed with 100% infill I have found these plates to be sufficiently strong as is. The design will likely evolve as I experiment with the harness; for now this is a usable configuration. If you want to recreate the stl files from the openscad simply comment/uncomment the dorsal and lumbar module calls as needed - the plates are slightly too large to print both properly on a 200mm x 200mm bed, so I had to do them one at a time.