P-bass are much happier in groups. If you where dead set on trying a single one I would add some dithers to make him feel more comfortable. It also depends on the size it would be less traumatic for an adult pbass to be alone then it would for a juvie.
Personally, I think they look much better in pairs or groups. I've got four now and would like to add two more. I don't think they have the same impact visually when there is only one.