A few things:
1) I figured out the bungee cord/ring set up inside the tent (with all y'all's help - thank you!)
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2) I found a way to secure the AC mat to the inside tent deck without drilling into it. I used the strap for the provided mattress (w/Velcro, to keep it from flopping over when the tent gets folded). I stripped the Velcro off the webbing and used a ladder buckle, cut a small hole in the AC mat for the webbing to fit through, then back to the ladder buckle:
I also figured out, that after closing the tent with our sleeping bag inside (and a 2" memory foam pad), I'm going to add another buckling strap to the side of the tent that opens, to assist in controlling the tension from the stuffing. No photo yet, but it will look just like this:
Here's a look at the inside of the tent with the sleeping bag: