So here's what I'm gonna do: I made 3/4" birch rings. Still need an inch of depth, so I'm going to prop this up with dowels, stretch some fleece, and fiberglass it to the blue plastic piece. Then I'll add some chop mat to the whole thing for strength, and mount directly to the door metal. Then I will need to cut the grill off the door card, and fiberglass that higher as well. I do want to use it, because I don't trust passengers and I tend to rest my leg against it.
Also figured out the possible amp stand-off problem. I was apprehensive about using the plastic pieces, but I liked the look of them, so I snagged some brass pipe and cut it to fit inside, pounded it in, and voila, no more problems. @keep_hope_alive and @audiobaun led me to this.
Stained the top piece too. I'ts not the most even stain, but I like it