So, I've been contemplating this a lot, and something that keeps popping into my head is just using a Sonotube.
The Sonotube calc software says the sub will work fine in a downward firing config.
My options locally for Sonotubes are either 20" or 24" diameter. 20" would have to be over 5' tall, but 24" would be just over 3, which is much better. Now, the real question is the port. With a 24" Sonotube, a 10" port's velocity with 1000w is maxed at 16.5 m/s. However, that requires that the enclosure be larger than modeled by WinISD (11.2 cu ft vs 9.3 "ideal"). Would I be able to add acoustafill to reduce the volume and keep the port?
An 8" port means the sub wouldn't need to be as tall, but port velocity rises to 25 m/s.