Here is a photo of the shelf I installed forward of the water heater (which is removed currently). Everything is simply fastened with wood glue and air-driven trim nails. I didn't plan ahead enough to realize that I needed to get the shelf somewhere up in there before installing the upright leg closest to us. So I had to cut the shelf in half and install it in two pieces.

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Next photo is the storage space after repositioning the wires for the LP detector. I might make some sort of wood bumpers to protect the detector. I'm sure it needs to be kept open, not enclosed, though.

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Here is one of the cleats I put in to beef up the drawer hangers.
