I live in the republic and this website has some reviews of campsites that are useful.
http://www.ukcampsite.co.uk/sites/re...unty=S+Ireland
I have camped in one place in the north, castle archdale in county fermanagh which was very good.
In the south:
Leitrim - pub on site -
http://www.battlebridgecaravanandcamping.ie/
Sligo-standhill - basic but on the beach
http://www.sligocaravanandcamping.ie/
Roscommon - Lough key - probably the best for facilities -
http://loughkey.ie/
Kerry - if you get the weather, its beautiful but mind the midgies
http://www.camping-ireland.ie/parks/...t-caravan-park
As for ferries, I generally use stena line, into belfast from cairnryan. I find its an easier drive from the ne of england than going to holyhead. Of course that all depends on where you are heading in ireland. Send me a pm if you need more info