I'm going to hook up the rubicon 702 to an FI SSD12 with copper coils in a sealed enclosure 1.6 cubic feet. This amp has 700RMS watts. Now what should I set the low pass crossover frequency to? Should I set the subsonic filter? If so to what frequency and should I also set the boost?

in a sealed enclosure, as long as there are NO AIR LEAKS, you can leave the subsonic filter off or turned all the way down.

LPF, that's your choice, most people set it in between 50-90hz.

Bass boost - shouldn't have to ever be used. If you do not have an oscope, then just leave it turned off, otherwise you will probably induce clipping at whatever center frequency it's boosted at.

If you have an oscope, set the gains on your amp by checking every other frequency to ensure a perfect, flat output. If, at some notes the output starts to roll off, you can set bass boost in that area to recover the output but you won't see this unless u have an oscope.

Thanks for the thorough response. How should I test for air leaks?

play some music or a tone and just go around the box, looking and feeling for leaks. some people use baby powder or the like to kinda sprinkle around the edges and see if they blow out.

great idea with the baby powder....thanks.