The rebar mat is now tied and supported with plastic bar chairs. We had areas near the edges that went pretty deep. I decided it was easier to fill the hole with concrete over terra-firma as opposed to filling and compacting. In these deeper areas, we boosted the bar chairs with larger rocks. 3/4" x 18" smooth dowels are laid in thru holes in the end form. I cut 2" dia holes at 12" on center in the 2" x 6" form, then screwed on the backer blocks you see with 7/8" holes. This centralizes the dowels within the 2" holes behind them.