Step 1: I had placed them together to start with, to decide how I wanted to assemble them and placed x's where it wasn't necessary to paint. Pretty much, just to save on paint.
Step 2: On the outside I painted with magnetic paint and on the inside I painted a blue.
I cannot tell you the shade of blue for I mixed this blue with paints I had found in the garage of my home before this one. :)
Step 3: Decoupage.
I didn't bother with painting the back inside the boxes either, because this is where I planned to decoupage with pictures from car magazines.
Also, I did not use decoupage glue. You can mix one part water and one part glue for this.