I thought about using the polyurethane stuff but the window weld is only $15 from a local autoparts store and I needed it for some hood and roof glueing too. Next time I do it, I'll use the window weld again. I wouldn't mess around with the versions that don't require a caulking gun though as they are too runny. Also leave some air gaps for a little movement to keep noise levels down. If you don't there is still more give than the harder, likely louder, polyurethane.

That said, if you want to make a mold and produce polyurethane inserts to resale then polyurethane is the way to go.