We did Dublin and then straight down to Cork and then all along the west coast to Sligo and then heading back across country to Dublin.
The only real sensible Dublin option is the campsite at Camac Valley some way out of Dublin centre. Then you can spend whole days in Dublin not worrying about van security. Get a LEAP travel pass to make public transport travel easy and cheap.
Otherwise the the trip between Cork and Sligo was a complete wild camp job with plenty of water taps available along the coast at various harbours. And fantastic as the weather was the best Ireland had known since 1976. The only real issue was cassette disposal as nearly all the public loos on route had signs stating no motorhome disposal permitted. Most loos along the coast use septic tanks as public drainage is limited to large towns only. We used green fluid which is public loo friendly and carried the green bottle if questioned. Do not rely on public loos for water as they nearly all had the automatic hand wash facility and no tap. There are virtually no chemical disposal points even at harbours.
Motorhomecraic.com is the must visit site for Eire.