For trunk sub the only two applications that work are corner-loading or infinite baffle. The latter is cheaper. Look at what TMR and Kmarei did. If I didn't already have the custom enclosure I would go IB with a single 12.
Mobridge DA2 > JBL MS-8 > ARC XDi 600/4 > JBL Gti 408 Mids & Vifa OT19 Tweeters; PG Ti2 1600.5 > Morel HCW-10 & IDMax 15