Ron if you want to support a box holding a fixture with the raceway it must be with rigid and you must follow the rules of 314.23(F)
314.23(F) Raceway Supported Enclosures, with Devices, Luminaires (Fixtures), or Lampholders. An enclosure that contains a device(s) or supports a luminaire(s) [fixture(s)], lampholder, or other equipment and is supported by entering raceways shall not exceed 1650 cm3 (100 in.3) in size. It shall have threaded entries or have hubs identified for the purpose. It shall be supported by two or more conduits threaded wrenchtight into the enclosure or hubs. Each conduit shall be secured within 450 mm (18 in.) of the enclosure.
If you want to stay with PVC you will have to support the box some other way.
And then of course the inspector could get you on exposed to physical damage as Redsy has pointed out.
