You go, tool guy! Good show, Ken. Glad to see you had at it. I'll bet the kids would like you to leave it on he grass just like that, but fill it with sand!
With something so substantial (the vertical members) to nail/screw into at the corner joints, you could have saved some $$ and left out the metal brackets, but they won't hurt.
Ken's one of us now---"one of us, one of us, one of us!" (Ever see Todd Browning's "Freaks," from 1934??
Thou shalt not take SquareBobGodPants in vain. If you ain't got the $$, we ain't goin' nowhere.