Too bad about the vendor's support. After sale support has been one of the better features of the diy kits I have built from Bottlehead, Selah Audio, Sonic Frontiers, etc. I don't suppose some additional bracing could do anything but help as long as it doesn't change the internal volume of the enclosure. Today I installed the damping material in the enclosures and glued the back panels. I used the Parts Express eggcrate foam for the sides, tops and bottoms of the woofer sub enclosures but ran out (it took 8 sheets to do both speakers) so I used 3" fiberglass home insulation on the back panel.