I'm going to have to stop responding to this thread. I just noticed you use a propane grill. Even though it is a Weber Genesis (my guess with the plastic side table 1996) it is still blasphemy. I had to cook on one of those things today for my parents (dad's has the teak side table 1995). Got home and hugged my 5 Weber Kettles & Weber Smokey Mountain Bullets , then made dinner on one of them.
I have to go to Kazoo to retrieve an original WSMB from my nephew. It belonged to my dad, it is #14 of the original 175 built. Broke my heart to see it gone.
The copper you are using will last 10 of our life times. Unless your a really good tin knocker stick with the tin stuff. If you need to form an inside corner you can solder it or fill a heavy garbage bag 1/2 way with sand, you can then hammer it into place. Heavier copper you have to warm it a special way to hammer form it.
Tom