My friend and I are going to this years Anime North as Gaige and Kreig. I thought I would share my process on creating her lunchbox.
Step 1: Sand and Prime
I started off by sanding each side then priming it with latex primer.
Trace around the top lid of the box and make your rough pattern of your chosen design. Lightly add color as a guide for when you are really going to paint it.
Step 3: Paint
I wanted to start off with a layer of distressed red for some added detail. Two coats of burgundy paint, then used a stencil brush with black to distress it (using the dry brush technique) then lightly coated it with silver. After that, I cut out some strips of paper and made a cross cross pattern on the lid. I then painted overtop of the lid with Green, Red, Yellow, Blue and Purple in their respective triangle. Once this was dry, I painted claptrap.
Step 4: Finish
After that, a matte sealer is recommended, you don't want the paint to flake when you are running around the borderlands.