I have another approach to look for the cause of the problem.
Before I had finished the binding, I’ve create rule to do fetch the prices (My poste rule).
You could try this rule as well and look if that runs through.
The rule does also use the httpUtil (as did the bindings you tested), that way you are testing if the problem might be the https call (WeatherUnderground is http!).
Yes, I’m fishing in the blind!