I agree with you 100% on the looks of the commercially available flatbed bodies. Very nice styling on your design, it clearly adds a lot more work. Can you post a pic of how you handled the fuel filler?
Another thing that I don't like about the commercial designs is how high above the frame the top of the flat bed has to be in order to clear the tires. They're way higher up than the stock pickup bed.
For my "traditional" truck camper I only need a 4' x 8' flat section, so I have been seriously considering making my own "quasi-flatbed" with boxed-in cut-outs for tire clearance to keep my CG down. Looking at yours is inspiring me to revisit that notion!