(and it can be used as a bench)
Here it is. Done. I decided that building a whole new box made more sense than trying to rig something up with a "ready made" box that wasn't "ready" because it didn't fit. Too much time, effort, and energy to make retrofit it. Besides, if something goes wrong in the future, I'll have a lot more room to get in and fix it.
Those green things you see in the box? Those are the valves I had to replace first. They required the most trips to Home Depot because they were installed wrong in the first place by the builder. Then I repeated his mistake and had to figure it out. Then...I had to fix it.
See the nifty feature I added? The front of the box can be removed so I can reach in farther, if needed. This way, it doesn't matter how long my arms are.
Today...I fill in the hole.