If this is going to have nothing 'private' and not actually going to have a proper prototype would it not make more sense to just have the entire thing as an object literal? In the style:

    GOVUK.userSatisfaction = {
      cookieNameTakenSurvey: 'govuk_takenUserSatisfactionSurvey',
      setCookieTakenSurvey: function () { ... },
      ...
    }

Which could then be started with a slightly cleaner:

    GOVUK.userSatisfaction.randomlyShowSurveyBar();