Should fit most "8020" rigs, I think.
But definately works with:
Simlab GT1 Evo
https://sim-lab.eu/en-us/products/gt1-evo-sim-racing-cockpit-1

Prints as 2 parts:
top section to get a smooth surface for mouse to glide on
main body: print with curved side up

designed in Autodesk Fusion 360.
.f3d (Fustion 360 file format) included for you to edit for your own uses.

Tapered T section for a snug fit. You will probably need a rubber mallet to install.
I glued a wrist rest to help keep the mouse from falling out of the tray. Just search things like "Gel Keyboard Wrist Rest Mouse Pad Wrist Support"