Chatta,
I'm sure urethane can work, but make sure it's of a formulation that will withstand the temperatures of a hot tube. I received a used preamp once with urethane dampers and they were a sticky mess. No idea how long they'd been in use, but they weren't doing much damping by the time they got to me. I stick with silicone just because I know it's one material that will stand the heat.
David
I'm sure urethane can work, but make sure it's of a formulation that will withstand the temperatures of a hot tube. I received a used preamp once with urethane dampers and they were a sticky mess. No idea how long they'd been in use, but they weren't doing much damping by the time they got to me. I stick with silicone just because I know it's one material that will stand the heat.
David