adhesion to urathane tubing, steel and shrink tube mastic

I am looking for a way to make heat shrink tube mastic adhere to
urathane tubing.
I am building a sensor that is to be used for winter maintenance
vehicles (plow trucks). The sensor element is potted in a 3/4 inch
steel tube with a 24 inch wire extending to a connector. The wire is
protected by flexible tubing covering the wire from the sensor to a
connector. A piece of shrink tube connects the tubing to the
connector. The tubing needs to have good adhesion in the potting
material and to the mastic liner of the shrink tube.
The problem I am finding is that it is hard to find a compatible tube
that will adhere well to the potting material (Locktite urathane has
been selected at this time) and the mastic liner of the shrink tube. I
see poor "wetting" and adhesive strength of the surface of several
types of tubing to either the potting or the mastic.
I tried urathane and various rubber tubing (1/4 ID, 3/8 OD). Rubber
seems to adhere best to the mastic. I'd like to use a urathane tubing
material, but I can't get the mastic to give good peel strength.
Are there materials I should try that "prepare" the surface of the
urathane to allow good adhesion of a urethane material to the heat
activated mastic of shrink tube?