Looks like you have some pretty good advice here. Only one item was missed, which is that a subwoofer should be placed in such a way that when the woofer pushes on the air, the air pushing back on the woofer does not move the cabinet. If the cabinet moves, it will emit sound in some fashion different from what the manufacturer intended. That is pretty much the definition of distortion (except when the manufacturer intends distortion).

The "over the dead body mount" is not really good in that respect. It often solves the problem of acceptance and general positioning but allows an overall degradation of sound quality to creep in. One simply cannot get a subwoofer to keep from moving when positioned thusly. The "not in my living room" (or back yard, house, marriage or planet) approach is actually preferable from a high fidelity point of view. The drawback is that then the entire system must also go to that alternate location. Otherwise one will have a 5 or 7 system in one location with an unacceptable but definitely high fidelity 0.1 system in another location.