Did you read the post you referenced for your 'design'? The carbon fiber was ugly so he decided to paint it, and then couldn't overcome the sanding marks showing through so he couldn't paint it the color he wanted. That's why I'd use aluminum skinned plastic.
Get mill-finished aluminum, and then once it's built buff it out. It would look like an Airstream, easy-peasy. Then your 2" of insulation and finish it on the inside with insulative paint and top that with
Fire Retardant Paint, for safetys sake.
I don't know a lot about Aluminum sheeting but I would like to. Nothing is set in stone and I have always loved the CampLite all aluminum RV's ! What is Aluminum skinned plastic ? What thickness of mill finished aluminum would you use for RV skin ? I do some pricing and see if thats a better way to go.
I sure the forum won't mind if we post a few more times on this subject because whatever I end up using will need to be formed into the best aerodynamic as possible. :-)