I want to cast a replacement seat bottom from a motorcycle. It appears to be originally nylon(?). The new part needs to be flexible, but rigid. The seat cover is stapled to the base so it can't be as hard and rigid as epoxy or fiberglass. I live in SoCal and have been looking at some Smooth-On products: Smooth Cast 45D or Smooth Cast 300. I am not limited to this product. Other than the stated requirements, I need about a 20 min pot life, want to keep the cost under $80/gal (I know the products I mentioned cost more), hopefully available in CA to keep shipping costs down. Any ideas or suggestions?