Karen, glad to have company on this PVC journey ! I did put a half inch diameter pvc pipe down the center for watering. I drilled a bunch of holes in it, hoping I can distribute water evenly. I agree, you really do have to water gently or loose your potting soil.
I'm shopping for a couple more plants to fill in where the verbina died.
I also drilled holes in a plastic half barrel, that setup is doing way better.