That is a really good tip on the nuts. I use blind nuts myself, but for those that don't like using them, this is the next best thing.
I like the idea with the gift cards as well. I usually use a backup piece of foam on the inside to do this same thing, but as you have guessed, it doubles the size of the wall and can take up too much space.
Can't wait to see this thing in the air. I'm still working on how to fix the issue with the ESC and battery. I'm hoping to have a solution here soon. Now get that thing in the air!!! hehe.