As I'd only just put a new tank on mine I dropped it enough to stick the pad on top, I put it on the top as thought it would eventually become detached if on underside, I'm not sure but think I may have stuck one on the bottom as well to start with, but it's certainly not there now, but most don't have this problem, no one else has mentioned it anyway, most people in the car didn't even notice, maybe it's my cossie paranoia!!
The std one can be poly filled, my mate did a few for me, one of which is in Iceland on a 1/4 mile sprint car, it's been perfect, how long would it last ?, it would outlast the normal type of poly rear imo, it simply adds resistance to the std one so no fitting issues, and last one cost me £25 to do, the mount is sealed on one side, then held so the top surface is level, then filled with poly slowly so no air bubbles, and allowed to set, makes a massive difference to stiffness, over a much much larger area than the "std" poly type.
tabetha