This driver is good for a QWTL (quarterwave transmission line).
Acoustic transmission line - Wikipedia, the free encyclopedia
Transmission Line Speakers
Quarter Wavelength Loudspeaker Design
A 4th order bandpass can give you more ~4dB but is restricted in frequency, good when you crossover at ~80Hz.
In an easy bass-reflex (BR) you can use an ideal 43 L int. volume alignment, with f3 28Hz-ff/20Hz-in room.
JBL GTO 1002D, VB = 43.3 L, FB = 19.7 Hz
(Note: now the problem with this alignment is that for Port you need a 3" internal with length 77.15cm = 30 3⁄8in.)
So if we change to another alignment say (with f3 21Hz in room)
JBL GTO 1002D, VB = 40.0 L, FB = 22.0 Hz
we have a Port 3" int diam and with length 66.2cm = 26 1⁄16in.
As you see (you can simulate your desired alignment with any software, use WinISD or UNIBOX) now the constraint is the length of the port. For that matter another alignment with higher Fb or shorter port length (Vol=50 L f3=20Hz in room).
JBL GTO 1002D, VB = 50.0 L, FB = 23.0 Hz
Port int. diam. 7.62cm = 3in
Port lenght 45.88cm = 18 1⁄16in
I'm sure you would be fine with this type of port size/máx.lenght (FB ~ 23.0 Hz) for the box volume ~50 L.
Precision Port 3" Flared Port Tube Kit 268-350