I made mine sealed boxes - due to the smaller volume required. the boxes were actually smashed speaker boxes I reworked. The factory subs are free air type, so you can use either method IIRC.

If the amps are in fact Alpine 3554's, then you will have 150w RMS x 2 (bridged & 4 ohms) for the subs, bit less because they are 6ohms.

Depends on the ford part no as to how much adjustment you have.

What's your no ?? Should be something like 94DA18T805 xx

Ah ok. I was thinking sealed anyway. What sort of box measurments would i be looking at for setting up the 2?
Alright. That looks like decent power for these subs. Do the ohms go down when you add the second sub because I thought they run at 6 Ω, or is this a max reading?
The ford no is: 94DA18T805AA