I have heard that River Valley gets *very* full and noisy over bank holiday weekends, so you may not get a representative experience of camping in general. I dropped on one bank holiday Monday and it certainly seemed to be very full. The facilities looked very good, but to be honest overall it seemed just too big to be enjoyable.
There is a great campsite down by the beach in Kilmuckridge in Wexford, but they seem to be anti-tent in that they claim to have one tent pitch in a field that can take about 80 or more campervans and caravans, but it would be worth giving them a shout. They also have mobiles on site, but I'm not sure if they are private or for rent. The site itself is basic, but you cannot beat the beach access as it is right behind the dunes. You would need transport around the area as it is somewhat remote.
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