solution:
step 1, remove spare tire, jack, carpet, anything else in area
step 2, get angle grinder and griding disk, cut the damn mounting block hump thing out. use of BFH is probably necessary and very gratifying.
step 3, install stereo system with well fitting box in area. it wont move around, make noise, and is probably lighter than the spare and jack
i took my spare out once, never got it to sit right again, gave up.