I couldn't tell from your picture, but....
I made a set similar to those a couple of years ago. One thing I did that worked pretty slick was to lay the boards(when finished) back to back and clasp them together by buying four clasps at menards that are similar to what you might see on an old school suitcase. Because I supported the middle of the boards from underneath with a 2x4 like you mentioned with the 2" cedar, when put back to back the 2x4's from each board created a little storage area for the bags without worry of them falling out of the holes. I slapped a handle on the side and have been carrying it all over the place for the past several years. They were a first generation model if you will, but I've got plans for a new set before football season with a new lighter and more durable design. Hope this made sense....
Good Luck!