Let me see if I understand--each pair of legs is attached to a 2x6 to make a three-quarter-rectangle, and that center 2x6 is attached parallel to one of the cross braces. Right?
Where did you get the neoprene cover?
Correct, the 2x6 is cut with a notch at the bottom corners so that the table leg sits in it and extends underneath the table skirt. The skirt rests directly on the exposed part of the table leg in addition to being attached by bolts from the table joist to the 2x6 that joins the legs on opposite sides. The leg "sets" aren't currently joined but will be joined by a shelf 12" up from the ground.
The neoprene cover was from Foamorder.com. It was 6mm because that is the only thickness they had the forest green in. I was originally planning to use 2 or 3mm neoprene and save a bunch of money but once I was that far in I wanted what I wanted. At this point if I had to do it again I'd probably order the double sided green/red neoprene from Moodfabrics. It's 2.5mm and much less expensive.
I was originally also worried about having fabric on both sides because I didn't want the mat to slide around, but my design actually has a separate frame that goes over the neoprene and holds the mat in place (and also covers up the pocket hole screws and will support the inset leaves)