I found some insulation that was very thin but had a rating of R8 which was pretty good for the thickness. The roll was 40$ for 25 feet, it was much cheaper than using regular insulation with Tyvek. See attached pictures.
I ended up replacing the tail lights due to the condition of the original ones. It was just a better solution. The next step is making sure all my running lights are working properly then finally attaching the last skin section.
Its interesting to see that my rebuild of the entire back sections with no directions was very close to the original specifications. I would have to say that I was about 1/8in and some places spot on.
Here is my check list:
All rot removed, and wood replaced, existing wood treated
Bathroom exterior walls complete
Back walls rebuilt, installed and insulated.
Tail Lights re-wired
New Taillights installed
Old curtains – out