Requirements for Surface mount raceway using THHN
I use raceway quite often.  With a 20% max fill and no need to derate if your current carrying conductors are less than 30 total it is easier to lay cables in than pull in some cases and no derate is the big advantage.
For exterior raceway it will need to be listed for sunlight or UV protected I have used pvc in the past but most of my work is heavy industrial where metal is needed to protect from impacts. Metal holds up better better but in your case a plastic wire way makes sense to me.