Nice job, what's the bike?
I had a tackle box that was buffed stainless and ended up having to burnish it because out on the water, every now and then the reflection would knock me down!
I see a parallel-twin, Yamaha XS 650?
I wondered if it was going to be a below the seat side panel, aft of what used to be for the carburetors, to cover-up the battery compartment and the electrics. Then I saw the detail pic. So, yes it is for a side-panel, and well-crafted.
With the rubber grommets, it should not fracture.
As a complement to your metal-working, here are some examples of my since-childhood friend's metalwork. He is well known on HAMB, and while he normally does custom chassis and exhausts for various $$$$ projects, he can also do bodywork. It's all-metal: fenders, side covers, gas tank and seat.


