Grant - never heard of it before. Where can it be bought? Halfords type places, or more speciality?

I know of Rain X but was under the impression that while it does work, it's pretty weak stuff when it comes to longevity; it wears off quite quickly, especially with pressure washing. I generally get the car washed by the local hand wash place once a month / 6 weeks or so - would I need to reapply Rain X after everytime?