I've been working on other projects, but I have made the template, finalized the design, and picked up a piece of plywood 1/2"x18"x48". You may want to use a narrower piece depending on how far back you position your passenger seat. 18" just touches my seat.
I determined that I will need to hinge the shelf to be able to get it in and out of the car. I will cut the plywood to the template shape (so that it sits on the little ledge) and then temporarily mount a piece of piano hinge along the centerline (front to back). I will remove the hinge and cut the shelf in half. Then reattach the hinge. I haven't decided if the hinge should be on top or bottom - that will depend on which way is easier to fold the shelf when installing and removing it -- the shelf can simply be turned over to position the hinge.
I will use two pieces of wood to support the shelf -- they will fit into the slots that are used by the OEM cargo cover rods. The wood will be sized so that it sits level with the ledge -
There will be some wood cleats on the bottom of the shelf -- they will hold the shelf from sliding forward/back on the wood supports.
I will attach the carpet and slit it along the hinge line. I also might attach a piece of 1x4 wood along the front edge to keep the dogs from sliding off the edge.
That's about it. Hopefully that will help you get started.
Did you get that shelf built? How about a photo if you did. I'll need one soon. I am picking up an orphan on Saturday, the 11th, then Molly, Max, and I can cruise. First stop - PetSmart with the SmartPets.
They are the best - no doubt! But you better love being sat upon... a lot! Right now Molly(right) is on my lap as I "try" to type. Max is wondering where his space is. Do yours like riding in your smart?