I was trying to come up with a way to fill the gaps in the corners of the frame but nothing really worked. I then came across a product called Bondic. Bondic is a clear resin that cures with ultraviolet light. Once cured, it can be sanded, polished, drilled, tapped, painted etc. It is not a glue, you can actually make things with it and the website explains more on how it works. https://notaglue.com/
The orange piece on the end of the tube is the ultraviolet light. You literally dispense the resin and then shine the light on the resin for 4-8 seconds and it's cured!