The best polish for the aluminium finish is old fashioned Beeswax. It does work and does not take off the paint.Only ever used a PTG a few times in the past. Do they work on painted aluminium??????
The arguments about best polish seems to recur every few months. After all usin "T" cut etc will make your van look clean with little effort but once every ten years is perhaps enough.
I have been using Meguairs polish that is used on glass fibre Gel coats in marine circles and it seems to do a good job without taking off too much paint. I might try beeswax over larger areas to see if it works.
Alan