Thanks for the info.
Purchased 6 mil plastic at Home Depot which is at least as thick as what's behind the wallboard now and it was the only product that specifically said it was for vapor barriers, moisture barriers, etc. so I should be good there.
I know exactly what you mean about duct tape based on past experience over the years. I recently installed new 6" ductwork in the attic for two bath fans and knew to stay away from duct tape, so I used foil tape instead. From what I can tell, foil tape has the same qualities of sheathing tape except for the 1.44 mil aluminum foil backing. But it's extremely durable and says it's perfect to use as a moisture barrier. Not sure what you think of this but I was considering using the left over foil tape to seal the vapor barrier behind the walls since the areas which need taped are flat. Otherwise I'll check a few more local places today. I could order it online but don't want the delay unless you (or someone else) thinks the foil tape is a bad idea.