See my youtube... Airgapped reflectix closest to van metal, then spray foamed foamular, cavities filled in with polyester fiber, floor has radiant barrier with air gap too, I made a video on it
The walls were filled with 1" hard foam and held in place with expansion foam. If I were to do this again I would elect to use spray foam instead, the time savings alone would be worth it. The paneling is 1/4" plywood with a good face.
https://www.homedepot.com/p/100549260
CheapMessy and time consuming
Click vinyl flooring
Would NOT recommend. It was a pain and has definitely shifted/popped up in spots. If we did it again we’d use a single piece of sheet vinyl.