Nice work, Tru. I wasn't quite following you when you put up that metal cover but now I get it! Looks like a very useful structure, not to mention, it looks a lot bigger now that it has some stuff in it. What a good idea adding on to it. I didn't even think of that.
I wouldn't worry about the end walls, you have to always have another project to work on anyway.
Besides, it hardly gets cold down there!
"Knowledge is power. Arm yourself."