I've made some good progress. The innards are all complete.
I had to wait for the pvc cement on my pH probe/injection manifold to dry overnight, but then it was easy enough to install:
Had one little hang-up..... I for the outside boards are 1/2", so that the 3/4" screw I used to mount the manifold ended up being about 1/4" too long:
Later on I'll cut that off and fill the whole in, but not today.
The manifold is then hooked up like this.
The pH probe has to stay wet, so it can't be installed until the very end, but you can see the co2 line installed in the irrigation fitting.
The final construction of the inside goes a little something like this:
And I'm ready for the next part: