Portumna is a good spot. Good playground in the village which is a short walk from the harbour. The harbour also gives you easy access to the Forest Park which is great for walking and cycling. Village has felt the brunt of the recession and the fire damaged hotel is a real loss but there are still some good places to eat, a good supermarket and a good hardware store which sells propane.
http://goo.gl/maps/MHKgN
Pull up on the right but face the harbour wall (not like the guy in the picture) as it can get very busy (10+ vans) on a summers weekend. No problem overnight parking here. There are signs requesting campervans to not park beside the harbour wall which is more than reasonable.
There is a toilet block but it is not up to the standard of Terryglass. AFAIK Waterways Ireland have recently taken over the harbour area from GCC and have a development plan in place. Apparently they also have the money!