I've been a ground shooter for a lot of years. I took the lazy way out and bought a Skimmer II. I was hesitant at first to pay for a ground pod since I had seen units fabricated from skillets, etc. for considerably less money. I was concerned about weight since I hike often with my gear to get get to my shoot locations, many times in the summer months here in the southeast. The 500L, Wimberley II, tripod and pocket accessories brought the total weight up quick. So with weight being important I went with the Skimmer II. I've never had a single regret in my choice, it's by far the most-used accessory I have.
Evan, I understand you wanting to get lower to the ground but I find myself more often wishing I was up a bit higher. When the shooting surface is very flat lower would be nice, but when the surface is uneven I often lose sight of the birds feet. I prefer to include the birds feet in my shots whenever possible. Also, the lower the camera gets the more difficult it is to align your eye to the viewfinder and harder it becomes to use your elbows for support. My lens sits on the Wimberley II(see photo below). If I were to replace my lens foot with one from RRS I could thread the Skimmer right to the lens foot which would place the lens hood about 2 inches or so above the ground. I personally would not want to give up the gimbal head, it's invaluable having that ease (and silence) of motion. With the lens foot attached to the Skimmer, vertical movement could only be made by tilting the ground pod and stability while shooting would really suffer. There's always a need to tweak composition vertically and horizontally and the gimbal is perfect for that.
badams, I wear a thin nylon pant and jacket that has a water repellant coating on the inside. Great for staying dry and keeping the sand out of your pockets. The sand and dirt brush off with ease, even when damp the material dries quickly(especially in the sun and breeze) and everything brushes right off.