It is entirely up to you. Click on my avatar and look at my album.
You use short screws like 1" and smaller when mounting to a rear seat.
133whp-126ftlbsTQ Eclipse CD8443,JBL Px300.4, JBL GTO7001, PPI 356cs, JBL p1024(Hooray!) SubThump enclosure, RAAmat BXT, Damplifier Pro
Hatch Nation #140
Caeci caecos ducentes