Robin,
You dont HAVE to use a CAMO for managing maintenance - it just reads a bit easier at the moment.
DFC has pointed out an owner can do this if he deems himself competent. As I've said before that is a matter for the owners technical competency, his wallet, his technical library, his conscience, & the Board of Enquiry in the event.
This puts you outside the "controlled environment", and then you will only need the CAMO with ARC revalidation privileges (or otherwise go to the CAA) to carry out the Airworthiness review each year - effectively a C of A renewal every year.
If you do use a CAMO to manage maintenance, then you are in the controlled environment, they can approve certain tasks an owner can do. The plus here is that then you can have two CAMO issued extensions to your Airworthiness Review, so a bit similar to the current M3 renewal process, just paying for yet another approval and its upkeep to do the same as at present.
Best Regards
Malcom