So back in the late 70's, my guitar teacher (serious cat: musical director for TOny Orlando, Cher, Lou Rawls, and actually fired Jaco from the the Lou Rawls band for not playing what was in the book) took a Gibson 335 and sprayed it full of foam so it wouldn't feed back on stage. I'll bet he'd have rather shelled out the $8 at the time (adjusted negatively for inflation, of course) for that somesuch piece of rubber.