I have used a product called Bow-to-Stern on my 2016 1685 from the beginning (it was mentioned in LOA discussions back when I was wondering what to use). It applies very easily, has protected the surfaces well from aging in the sun, and is designed for fiberglass boat protection which makes it well suited for the both the sides and front of the trailer since they are really plastic products. It produces a nice shine after about the third application, less so until then, but bugs and things smashing the front of the trailer come off easily because of the finish. The same company also produces a cleaner for the more stubborn stuff as BTS itself does not clean the surface much, just protects it. https://www.btsproducts.com/
My brother-in-law asked me what I used on my trailer to keep the exterior looking good. He had been using car waxes and they just did not protect the surfaces as well. Now, I only have four years of experience with the stuff so far, but it does seem to slow down the inevitable aging of exterior surfaces in the sun.
I apply it a couple of times a year, easy on, easy off, and it keeps everything looking good.