Just buy a pre constructed access panel at any hardware store and cut out the back of the cabinet to install it.

That's what my guys did, too. It's a plastic frame and panel that you fit into a drywall opening and it stays connected through a spring type mechanism and tabs. Mine is in the back wall of a closet that abuts the plumbing wall. I also have one for the shower and tub drain in the kitchen ceiling (which is a little annoying visually, but I'm fine with it).

great help. Do I need to have it run from the valve/controls, up to include the shower head junction? Oatey makes one that is about 14x29" that might include all these areas. Or do I put 2 smaller ones in, one at the valve/controls and another at the shower head area. There are Hansgrohe iBoxes in both these areas. There is also a Quattro valve near the lower iBox. Nothing is in yet but will be by weeks end.

Thanks

Mine is about that size but centered over the main plumbing area by the thermostatic mixing valve, volume controls, and body sprays. It doesn't quite reach up to the shower head, but that's the area least likely to need replacement, etc.

Kevin, good to know. I will be calling my plumber today to find out what he suggest in the way of sizing. I like the idea of having it all accessible, even the shower head. maybe I could put in a small one up there.

I talked to my plumber and he suggested that I just leave the area from the controls up to the shower head iBox exposed since a cabinet is going there. I might just do that. If there was a need to cut through the cabinet it would be helpful to have is hollow on the other side instead of a plastic panel.

The other thought I had was to have the cabinet made with a large opening in it's side that would encircle the access area, then I could put a removable panel in the area made out of drywall or by an Oakly access panel if I can get one big enough.