AlpineRAM

Did you paint them after polishing?
The polycarbonate needs some UV protection to keep it from yellowing. I've had mediocre success with carnauba wax, it would keep them OK for about 10 months until the yellow came back, much longer if the wax was renewed every 3 months..
The clear coat with UV protection usually works for 3-5 years for me, main problem is the stones chip away the paint.. also on the bumper, the grill, the hood etc..

KATOOM

I never clear coated them but I did wax them, repeatedly. And my truck sits in the garage 90% of its life too. Strangely the side turning light lens is as clear as the day it rolled off the assembly line. Too bad Mopar didnt have their supplier simply make the headlights out of the same plastic as the turn lights...

AlpineRAM

Mine is in the open air and sun all year long..
But the side marker being OK when the headlight is not- just a question of temperature.
Maybe your less than good results with wax are due to the wrong wax for the job?

KATOOM

Possibly...
I still have the factory assemblies sitting in a box. If I find myself with nothing to do some day I might take the time to polish, clear coat, and wax them again.