8020 has designed specific panel brackets (retainers) for fastening panels to 8020 profiles as inset panels. These panel brackets have a standard bolt hole on one side, and a threaded hole on the other end [hardware list below]. The bolt hole side is for attaching the bracket to your profile with a bolt and t-nut. While, the threaded bolt hole is for attaching to your panel. In order to achieve perfect inset panels, you should cut your panel 1/16″ to 1/8″ inch smaller than your X-Y opening. The tighter the better, of course, but with wood, you also want to keep in mind that it will expand so somewhere in the above range should be good.
To install inset panels, measure where your panel brackets are, and drill holes through your panel in the appropriate location. Additionally, for a clean and finished look, use a countersink drill bit to recess your bolt head into the panel. Your bolt hole size can be 1/16″ of an inch larger than your bolt size.