I wanted a spoilboard for my newest Genmitsu 3020 PRO-MAX cnc router that was:

• mist coolant-resistant, when machining metals (so no MDF, plywood and such);
• crystal-clear, to keep the grid on the underlying stock working bed visible;

Having a laser cutting machine, I made it that way using a 4 mm thick acrylic sheet.
Obviously, you can use whatever method you prefer, I.e. cnc milling, 3D printing (less recommended) or manual drilling using the measures I took as a reference jig.

NOTE: After the first prototype of the board, I noticed the 3rd, 4th and 5th row of holes, uniformly spaced in my design, were not perfectly aligned with the threaded holes on 3020 pro-max working bed. Whether is something related to all 3020 pro-max or just my own machine only, a feedback on this issue from SainSmart/Genmitsu guys or other 3020 pro-max owners would be quite beneficial for all, I guess…

TIP: I saw guys on YouTube glueing their spoil boards to the working bed. I prefer using screws. If you like them too, I suggest to use 4 conical head M6 screws, one for each corner (just countersink a bit the related holes on the spoil board). This way, you’ve got tight bond + whole flat surface. By the way, provided .stl is already countersunk on every hole.

SainSmart Genmitsu 3020 PRO-MAX is a relatively new machine and there are few resources and mods out there yet.
Any improvement to my solution is more than welcome :-)