is there a certain distance the driver wants to be from the back of the enclosure or is it fine anywhere as long as the correct amount of volume inside the box is present?

also, is there any advantage to buying a dual voice coil sub over a single voice coil?

Depending if the woofer has a rear vented pole you want to at least keep 3" between wall and rear vent.

Dual voice coils have more flexibilty than single.

"also, is there any advantage to buying a dual voice coil sub over a single voice coil? " Is dependent upon how many subs you plan to run and the capability of your amp.

"also, is there any advantage to buying a dual voice coil sub over a single voice coil? " Is dependent upon how many subs you plan to run and the capability of your amp.

i plan on running two fi bl 15"s on one sundown saz 1000d, eventually two..

Check out this "wiring Program" and see if it helps your understanding on the ohm loads for the amp. Subwoofer Wiring Diagrams