I contacted ReWo last week, and they explained they are no longer producing the GH2 cage. So if you find one it's like gold. You might want to look at the D|Cage. I use a Gini Cage and it seems to function pretty well. It's only $250 or so from camera 777 with a couple of 15mm rails and handles. The D|Cage alone is around $350.
Shame about the rewo. I like the look of the D|Focus cage but I cannot see how I might fix this to a rail system for shoulder mounting and use of FF and MB. the rewo already ha this covered.
The Gini Rig cage I bought came with a pair of 6" rails on the top. I added a FF, and for my zoom lens I added the $50 Follow Focus to control it. They are both on the top, but it works quite well! The newest version of the Gini Cage also has two tabs to keep the camera from rotating in the cage.