Bass Traps = MINIMUM 4" thick, 24" wide rigid fiberglass panels(or other mineral fiber), 3lb density, straddled across as many corners as you can, min width 24"(preferably floor to ceiling at wall to wall corners). Fill behind with R-30 or if you can afford it, stack diagonals of same rigid fiberglass. Do search on "Superchunks". Cover with any fabric you can blow through easily, or make fabric covered frames.
Forget auto insulation for bass traps.
rigid fiberglass panel= Owens Corning 703, Knauf or other (be sure it's 3lb density)