I'm just starting 2 of them today. I like to use the tricot iron on interfacing. You alternate the stretch of the tricot going one direction and the stretch of the shirt the other. I think it gives it a nice body, but not too hard to quilt thru. I have quilted thru the shirts too..but beware of shirts with lots of stiff paint. Try to plan your quilting around that. Here is a picture of one I am using as an idea. I love the way the blocks look like they are 'floating' on top of the quilt. Fools your eye doesn't it? lol
I hope it is not too small to see.
Let me know if you want more info on this setting.