Here's a side view of one of the burners. The Hardibacker does a good job of keeping heat away from the wood. I made straight cuts through the angle iron and notched the wood. Haven't seen any sagging so far.
I do need to block off some of the tips in the burner - the flame is hard to control with all 23 tips on. I keep getting a small flame in the base of each tip where the air is supposed to be mixed with the gas and it starts burning yellow. I think enough of the gas is combusting in the base of the tip to make the mixture at the output of the tip too "lean" and causing the yellow flame. Blocking off some of the tips should increase the pressure and prevent the flame at the base of the tip. I've seen the thread about blocking off some of the tips and will try that.