I was doing a rework of my workshop and had an old muscle rack that i thought could make a good table for my printers, i designed this bracket to allow me to use a few countersunk wood screws to attach a work surface. It should also work on the many clones of muscle racks seeing as they all use similar dimensions. Just slot the brackets onto each corner, place a surface on top and install some screws. You may need an extension on your drill/impact driver.
You absolutely need to print this with at least 4 walls, 5 top and bottom layers and at least 25% infill, use an appropriately strong and rigid material and optimize your print settings for layer adhesion, in my case i used petg with part cooling turned off and printed at 260c.   

I hope this is useful to someone!