Isolation of a sump pump vibration?

Hi, I'm trying to find a simple way to isolate the vibrations of the pump from the bucket. I had great success by putting folded up rubber pads under each leg but it wasn't stable enough. I think that a nice piece of 3/4" neoprene rubber would work (maybe with a plastic sheet on top) but I can't find a company to sell me a piece that small. Is there anything I could find at a Home Depot that will work and stay intact in water? Thanks, RichR.