No it isn't oxidation on a 2018. Aluminum oxidation typically occurs on vintage trailers - it turns them from "bright & shiny" aluminum, to a dull flat grey.
"Vintage" trailers either have failing clear coat, no clearcoat ever or stripped aluminum which allows the elements to oxidize and it turn dull. If it looks splotchy (like a sunburn) it has failed clearcoat - as the clear coat fails, it oxidizes in phases over years, which causes the splotches.
"Modern" trailers have a thicker plastic-coat that is supposed to protect the aluminum from oxidizing. Your photo looks like it might be just hard water spots on the plastic-coat, in which case, vinegar/water will help remove them - as will Walbernize or a spray-on car wash formula you would use on your car.
If it is a white crusty/powdery residue, it could
be the start of filiform corrosion where tiny breeches in the plasti-coat film has allowed water to get in behind
it. The resulting moisture can't escape and the aluminum starts to corrode - which is what causes the crusty/powdery residue.
I would try the vinegar/water in a small area - if it works, then proceed with the whole trailer.