The over the well jl stealth boxes are really good. You could build one similar and not lose a ton of space and ensure no rattles. Pretty low effort compared to dudes building those super stealth ones that involve panel removalI'm also throwing in the towel but because those rear panels just resonate and rattle like crazy with the output from my JL 6" W3, would take a ton of deadening and might still not be enough bc the glass is rattling as well. Gonna move it to a small ported box in the back cargo area, found a great box on Ebay, tuned to JL specs, it's not much bigger than a large shoebox.
JL Audio Stealthbox®
Custom-fit fiberglass enclosure with 10" 10TW3-D4 subwoofer — fits 2010-13 Toyota 4Runner vehicles
www.crutchfield.com