What kind of box do you have ? Maybe it is too big ?
I switched mine too :I had a 3.5 ft3 L ported box for my SSA Xcon, and it was taking all my cargo area.
Now I have a 3.1 ft3 ported box with 2 x 4" aeroports(flared), and now it sounds much better, takes less room, and it's even louder (port is firing to the side, instead of firing up).
I would not put a BTL in a sealed box.
You can get it rebuild to a 12" , so that you can use a smaller box.
Good luck !