Feedback for my setup?

[Tuxer]

Alright, I've been piecing together a setup for my 01 Toyota Tundra Access Cab for quite some time now and am ready to move forward but would like your feedback. I've been out of the car audio game for a few years and feel rusty as hell. I imagine I'll only have the truck for 2, maybe 3 more years before I upgrade so it's more of a temporary solution with potential to carry over. I'm on a tight budget as well which doesn't help my cause, but I'm dying for a system again.

Placement: I've got an 8 year old daughter, so the back seat is important and need as much room as I can. I'll be folding up the seat behind the driver and putting the subwoofer box there. If I need both back seats, I'll move it in between the two seats where cup holders/arm rest fold out (12" wide, 16" deep).

Subwoofer: Decided on the Sundown Audio SD-2 10" D4 (I'm actually still up in the air with the 8, but will likely go with the 10) (Linky)

Amp: RF Prime R500X1D (Linky) | 500w X 1@2ohm

Wiring: 4ga power w/ 50a fuse, standard RCA, remote lead and speaker (Local Shop)

Box (If I go 10"): Sealed | 9" (H) x 11" (W) x 15.5" (D) = .58 cu.ft. before displacement (.5 after) | 3/4" MDF

Box (If I go 8"): Sealed | 7" (H) x 10" (W) x 13.5" (D) = .32 cu.ft. before displacement (.25 after) | 3/4" MDF

Subwoofer will be down-firing, so I'll be building the box similar to this Pioneer. My original plan was with a Hifonics Zeus or Brutus amp to push more power for less out of pocket, but a number of threads here deterred me from that route.

And... Has anyone run these subs in a smaller box environment? Can I use 5/8" MDF instead of 3/4 or will the sub just break it apart? In your opinion, running just one of these, will there be a large difference between the two?

Thanks in advance for responses!