Are you noticing a microphonic feedback? (Why do you believe isolation would help?)
Under heavy low bass anything (and perhaps everything) in the room could be resonating. Removing objects would reveal if this is what you're hearing.
Turning the da*m volume down (your old man talking
) would help too.
Is the vibrations from the sub coming via a flexible floor (probably) or the air? I say "probably" because vibrations travel much more efficiently via solids than gases.
In either case adding mass to the amp (and source) would be helpful.
Adding dampening materials to the amp (and source) cabinets would be helpful in either case, but especially if the vibration transmission is air borne.
Some have reported success cutting racketballs or tennis balls in half and using them as isolation feet. Obviously these trial and error guesses are dependent on many factors (mostly component mass and the frequency(ies) involved).
The retail platforms are designed essentially try to act as frequency filters by using one or more materials/masses that are designed to absorb vibrations. If the component is coupled (use of spikes) to the platform the added mass also helps.
But just building a wooden platform with stiff rubber feet to sit the amp on probably won't help.
Note that wooden floors over crawl spaces can create some of the nastiest bass resonantors on the planet.
Mass and stiffness are your friends as they lower the resonant frequency and therefore increase the energy needed to start resonance. The soft feet and specially designed platforms shoot for filtering various frequencies. Sand beds and air bladders are primarily only frequency isolators.
