It's been dry so I've been working with wood. I realized to get everything level in the trunk I first have to have the sub box put together.
I started off making a template for the box's floor out of cardstock I found in the recycling bin.
I went to test fit the floor piece in the trunk and it wedged into where I wanted it to go on the first try. So I put the walls up (yes, there's gaps for now).