Long hill can be reached from lay-by above Barravakeen (first right past Clonmel golf club) at S248193 A with plenty of room for cars. Walk up the road, hop the fence and skirt across the top of the Punchbowl to reach the summit.
There is also easy access from Glennagad, via the road up to the holy cross (S209207 B - room for 4 cars). From this side there is a track up the mountain and then a quick trot across the boggy top to the cairn rewards you with excellent views. I suggest you stray off the track and look at the stone markers which can be found amongst the heather on the north of the track. These appear to be the remains of a firing range that was there some years ago. Linkback: https://mountainviews.ie/summit/807/comment/6773/