I ended up using the ERA mounting hardware, but moved it toward the center about 1.5 inches to clear my speakers. Works great with Optima battery. Also added a kill switch in the panel next to the battery.
You'll have a tough time accessing the hold-downs on either of the designs you're looking at. The ERA approach uses the chassis crossmember and a small piece of angle on top of the battery. Works well enough and you can get to it easily.