Looking good! I can't quite make it out but are your corners soldered on the galvanized pan? If it's not you can just run a bead of clear silicone up those corners if they're just spot welded.
It's been my experience (journeyman sheet metal worker) that any part of galvanized parts that no longer have galvanizing on them rust. It is just a coating on an iron sheet. I'd imagine it'll rust even more so around salt water. Any edges of the sheet, where it was cut to size, has exposed iron and will eventually rust. Just something you may want to consider. A coat of Tremclad would certainly help, but you'd have to pickle the galvanizing for the paint to stick. Easy as wiping the sheet down with vinegar.
Just a thought... I may be over thinking it
I do that, lol.