I used the same method that artists use.
I bought artists stretcher bars that cost less than $15, the lightweight kind. They fit together without any nailing or gluing. Then, I staple gunned blackout cloth to the frame, each staple a couple of inches apart. Also, make sure you have enough fabric to wrap around the back of the frame. if you end up with too much, you can aways cut it when you are done.
The real trick though is alternating sides, while moving from the center outward towards the corners. With each staple, you stretch it pretty firm, then go to opposite side, staple again, moving outwards.
If you are doing more or less 16:9, then you probably want to staple the long sides twice, for every one time you staple the short sides, since the long sides need a lot more staples.
The creases disappear in the middle and gradually migrate towards the corners, as you work your way out. Once you get the corners, you give it some final stretches, and your done, all your wrinkles disappear. Without a workshop, it helps to have two people do this. One to stretch and hold, the other to staple.
Worked for me beatifully. Now, I am going to do another one, this time with HCCV fabric, which isn't too expensive for a small screen.