I have 6 of these brand new in box. Purchased about a year ago, but the project I was planning never materialized.
I've had several of these Dayton Reference Series subwoofers in various sizes and configurations over the years, and they are really excellent for the price. Clean, deep bass that out performs subs 2-3x the cost. I've got a few of the 12" models that I've been using regularly for well over a decade, and they're all still going strong and sounding great. These things are without a doubt the budget kings.
Full details here:
https://www.parts-express.com/Dayton-Audio-RSS210HF-4-8-Reference-Series-HF-Subwoofer-4-Ohm-295-456
Happy to help if you have any questions about box size or port tuning as well.