While you do not need a DMM to set the LPF and the SSF, there are still correct ways to do it.
The placement of the SSF will rely on your enclosure. If it is ported, what is it ported to? If it is sealed then you can just leave it off.
The LPF should be somewhere in the 50-80Hz range, and that one you can play around with and where ever you feel sounds better for your subsonic bass you can choose.
Then try to aim your SSF somewhere between 30 and 35Hz. This will ensure that your driver(s) do not play too far below tuning, causing it to bottom out and potentially result in damage.