I am going a sightly different direction with mine, as it is shop-based and doesn't need to be portable. I want to be able to load a panel onto it in one part of the shop, then move it around the shop to wherever I want to break it down. Here's my concept so far:
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The table is 4' x 4' when closed, and opens to be about 4' by 90" or so. The supports slide in and out using wooden dovetails. The three slide parts are shown in color so it's easier for me to understand how they work.
My idea is that I can load a panel onto the cart, wheel it to wherever I want to break it down, and tip it up to be flat. There's a swinging lever that will automatically engage when you tilt the table up and lock it in place.
I'm still working out all of the details. Comments, suggestions, and criticisms are all welcome.