4th order vs vented wall

i have a 2001 expedition with:

2 DD 3515 CF

1 DD M3A

currently have a vented box subs firing up vent back.

going to do a rebuild this weekend and trying to decide between:

A fourth order with subs firing up into vented chamber with vented chamber firing forward, everything walled off behind the back seat.

A vented enclosure subs firing forward vent firing forward everything walled off.

my thought process is that if i wall off the space behind the back seat it reduces the amount of space to pressurize.

my main focus is daily listening but would like to see a nice number on the meter as well.