I have had an Elite gray nontensioned screen for five years. It has never developed a wrinkle. I believe one of the reasons is that the bottom bar is heavy.
It's just me, but before I started trying to convert to a nontensioned to a tensioned screen, I'd attach a heavy pole on the bottom and let it hang there for a couple weeks. I might also try to maybe glue lengths of cord to the back of the screen near the side edges, and pull them until the wrinkles were flat - and leave that a few weeks.
I think you could end up with an ugly result if you try to make it tensioned. I am pretty sure I couldn't do the job attractively.