so, added about 10lbs of mass with some killmat to the exterior
covered the outer rear with closed cell foam so it compressed to the body when bolted in
added some stuffing. bass now set to 0 for my taste [was at +3]
it's pretty good now. the enclosure doesn't resonate and that's a good thing. all that energy is now bass output
here is the impedance sweep and T/S measurements of the driver in enclosure, sorry i didn't have the stuff to measure the enclosure volume
https://imgur.com/a/K2ZOkvE