Have the Rockwood 2702 and wanted a "permanent" solution for my counter extension. Like many I didn't have a center wood bar to fasten to, so this is how it went down in case it helps others. I know there are a handful of counter extension posts already, but hopefully this is still helpful and not redundant.
Started here:
And here (minus the big bracket):
Went to this on the extension:
And this with brackets folded in:
This is how I worked the existing counter space:
Wife said I should have cleared all the "stuff" out for the pics, but just didn't want to bother.
The brackets are weight rated to 550lbs as a pair, but pretty sure if my 5 year old or 2 year old decides to hang from it it may go. Let's hope we don't test that. Goal was to get it full time mounted and be able to drop the leg as I think my kids will kick that out of place accidentally more than it will help support. Besides some play in the brackets themselves, feels pretty sturdy.