Here's what I did.
First I started with a bit of PVC pipe, a tee and an elbow.
Then I built a box around it like so.
The box is slightly taller than the Rat. The top of the tee is flush with the top edges of the box.
I fitted a couple of plugs (green) into the back of the extrusion, one either side of the dust opening in the Rat and a little ramp (blue) to direct all the dust into the tee.
I installed hooks on the front to hold the Rat and a top with an opening cut for the smaller diameter pipe.
The Rat is set so it is about 1/8" above the top of the top panel of the box. This helps to keep stuff from rolling off the box. The smaller diameter pipe receives a piece of flexible hose that can be positioned as needed when the main DC opening isn't effective. When not in use it gets a cap dropped over it to block the flow.
What isn't shown here is that I took a short length of 4" DC hose (8" or so) and clamped it to the bottom opening on the tee and installed a blast gate so my quick connect on the DC hose would fit easily.
The top was left off the box until it was mounted to the wall with lag screws into the studs. Then the top was put on witha a few screws. I put plastic packing tape on the underside of the top in way of the tee. Then I applied a bead of silicone sealant to the top edge of the tee and pet the lid down. The silicone forms a nice gasket but won't stick to the packing tape so the lid can be removed easily.
I didn't bother with the storage area but you could simply leave off the left end of the top or make it into a lid that slides or hinges out of the way.
Happy ratting.