Although unfamiliar with your urethane material, if it has a fairly soft surface hardness, then you might try micro-perforating the surface you wish to bond to.
I believe that Aerospace Composites in the USA would help here with some sort of roller having small pins protruding from the surface.
If the surface is hard, then you could do what we used to do. To adhere GRP to waxy plastics and angle-grind the surface lightly all over before applying a gel coat resin.
I hope this helps you.