Hi Scott,
Am a bit puzzled that it doesn't last in your experience. I see you mention leaving no protection after removing the damaged film, but if the routine in the link to Audizine is followed the last stage is to add the protection of a urethane varnish.
I looked at obtaining the same varnish a couple of years ago and failed as it seems the brand is in the North American market only.
In the end I purchased the 3M Headlight Restoration kit, which comes with a tiny sachet of their protectant in a 'wet wipe'.
I used this two summers back and the results are still as good as the day I did it.
I have polished up a cheap car badge where the clear coat has degraded and gone milky and then only applied car polish afterward. In this case the coating does start to turn milky again within a few months, but again I suspect if the urethane varnish / 3M protectant was applied it would be good for a very long time.
Nick