I saw your post when searching what others have done. I made a stainless box as seen below. It works but, I didn't have enough material for two boxes.
I looked for aluminum flashing at two big box stores but all I could find was galvanized material or painted material.
I ran across a bare aluminum gutter guard (Titan 5 in. x 3 ft. Aluminum K-Style Gutter Guard) which was available at both local box stores for ~$4.49.
I cut this to fit and VIOLA!, a dry run found it worked well. I'll stick with this under $5.00 solution for now.