If you don't get the mounting box from the builder (which is the best option), you could attach a panel inside the tank held by magnets. It looks like you have a lot of room under you tank (compared to my smaller tank), so could add the panel at one of stand ends and mount your devices to. I used neodymium magnets to hold to my stand. It ain't moving unless you need to remove - I like the ability to remove all panels and equipment. Here's a picture of what I mean without wrap, then with a rap I put over. This could work well with your space.
