Na, yours looks great. I like how you slanted it. I was going to but decided I had had enough with trying to figure out all these angles. I should have used an angle finder instead of eyeballing it, checking, adjusting, and so on.... I also, built mine to ensure I can still remove the OEM all weather mats and also access the storage bins. Good luck to ya, excited to see the results.
The area above my sub in the seat is pretty much hollow, but that's also why I added the grill. There are some benefits to downfiring, but you have to factor in the woofer's excursion height, and a good 1-2 inches of clearance beyond that for it to sound right. That would have left me with maybe 4 inches of mounting depth. So, so something to consider when you're planning. On the other hand, not sure if it's a good or bad thing (depending on male/female passenger) but up firing REALLY vibrates the seat above it. (flashback to the Howard stern movie) So there are some pros/cons to both.
I think the front of my box was 9", probably 10 or 11" if you slant it, so you could possibly do a forward firing 8" as well.