Not a PWC trailer, but I am working on a M101a2 army trailer that I'm converting to sort of a multi-purpose utility/ camp trailer. Expedition Portal is really a good resource, but I find over there that the "hobby" is more about building the trailer, than it is using the trailer LOL. I would say really take a serious look at what you need the trailer to do, how you plan to use it, and where your interest really lies (ie. the building out of the trailer, versus the use of the trailer).
Its like anything else, there's so many accessories and items that these forums will tell you that you need (ie. rooftop tent, Dometic Fridge, Maxxtraxx, Rotopax, $1000 awnings, etc. etc.) Best to really have a solid plan of what you want your trailer to do and how you plan to use it, so you don't get tempted to buy a bunch of sh#t you dont actually need or realize you'll never actually use!