Some years ago, in conjunction with the standard trailer ights, I put some on PVC poles. Used something like this LINK, mounted vertically.
The wiring was run down inside of the PVC posts. Doing that prevented the PVC posts from rotating, which is a great feature of PVC guide on posts. Rich
https://www.walmart.com/ip/Blazer-LED-Oval-Stop-Turn-and-Tail-Light-Kit-Red/15111219?findingMethod=rr