To avoid over complicating things and to stick to the KISS rule, how about the following modifications? Instead of one solid pieces, make the bottom support pieces separate cuts/breaks similar to the ORV brackets:



ORV Support Brackets:

 

I've been trying to work out what I want to do with my new JK and this has finally made it easier for me to work out what I will do. You idea for the wood over the back of the seats is what helped me the most.

 

I know this post thread is old but this design was exactly what i was looking for. I used some of your designs and tweaked it a little to work for me. So far i like how it cleans up the back end and makes my tools and equipment more secure from prying eyes. Taking it on an overland trip this weekend and can’t wait to see how it works! Thanks again for posting a great idea.