There is barely enough cubic room inside the spare for a 10” solobaric sub - I built that first before changing over to the freeair that was a much simpler design. That sealed box inside the spare was not easy to secure even though I carefully molded it to the rim. I also did not care for the solobaric sound. I’d love to loose the spare and get a 15” sealed unit back there but not willing to make that sacrifice - small spare is better is way better than no spare to me. Look forward to how your’s turns out.