Channel Surfing is documented with the USCG. As a result, she will never have WN numbers to display on the boat.
USCG documentation, I paid $750 to a title company and had them do all the paperwork. It took the USCG about 4 months before they issued our number. Ongoing, there's an additional $25/year that's paid directly to the USCG.
The documentation number is my registration number for the state of WA.
I still pay all state taxes, annually, directly to the state.
We had Channel Surfing documented purely out of aesthetics. We didn't want WN numbers on the front of the boat.
Letters on the stern must be 4" tall, and must include the hailing port. The documentation plaque must be affixed to the boat in such a way that if it were removed, it would be noticeable. It must also be affixed to a permanent structure of the boat (not like a door or a hatch which are easily removable).
All current models of Ranger Tugs (from The R23 on up) qualify for USCG documentation.