Hi Huckybabe, hope you're keeping well.
Im sure one of my friends went last year and raved about it, although she's not a motorhomer and stayed in a local B&B. I have had a look on their site (looks a great line up) and it says, Unauthorised Camping in Public Parks, Quays etc. will be Strictly Prohibited in Ballyshannon.
Bundoran is 3 miles from Ballyshannon and there are many Taxi Companies operating a 24 hour Service to and from Ballyshannon, as well as a Festival Shuttle Bus Service (11am to 3am)
There are a couple of campsites in Bundoran. we stayed in one a couple of years ago and i am sure we were able to walk into Ballyshannon.
Enjoy.
Dee