definitely good info, thats kind of what i was coming to with urethane, they would be too expensive, and i feel like the cracking in cold weather wouldn't be a huge issue, i don't think too many of us drive our cars when its THAT cold out.
edit: more good info, from my friends build...
"About 90% of the way through the install i discovered that these are made from a thermoplastic material, not thermoset. Urethane is a thermoset meaning it cannot be liquefied and still retain it's original properties. That said, the flares are ABS and are very easily molded with heat."