I used to own a plane that had metal wings glued together. The Grumman Tiger literally had aluminum wing skins bonded onto the plane. No rivets or screws. Th

I used to own a plane that had metal wings glued together. The Grumman Tiger literally had aluminum wing skins bonded onto the plane. No rivets or screws. They had some early issues with the glue they picked, but after picking a different glue it was a really reliable method. There are some of these planes flying still and are getting almost 50 years old. Many modern cars use the body panels as structural members because it is weight efficient, but trucks were probably the last category of automobile to adopt this trend. It is not necessarily bad design to have a separate frame, you just pay a weight penalty. Engineers may choose to do this because they have other design priorities than weight. Tl;dr: Glue is an okay design choice. Non-structural panels are an okay design choice. The Tesla engineers just didn’t get the details right.