As to shock absorbtion, you might want to consider rubber truck tire
chocks.
Thinking along the tire line, you might be able to find some small used
airplane tires. The ones with the thick walls that have some body to them.
Bolt them in between your float and the ends of the stiff-arms, using
back-up plates to keep them in place. Might not look great, but they
wouldn't rust, and are replaceable, and would be quiet, self-centering, and
would stretch in any direction. Drill a couple of drain holes in them to
keep mosquitoes from breeding in them.