The Trailblazer guide is excellent for identifying all campsites,as most of the farm sites are not actually adevertised as such on the route,although the information is a couple of years out of date,as the useful James' B&B in Prestatyn no longer allows camping.So,Prestayn is a problem location for camping at the start/finish.
Wild camping is more difficult than the PW, as there is less open moorland ground,but you should be able to find suitable locations with some pre-planning.Chepstow to Pandy and Bodfari to Prestatyn may be difficult, as it's mainly solid farmland,but if you are on a 6 day schedule,then you would'nt need to stop in those sections.