I totally agree with quiltingshorttimer about using a moist pressing cloth with fusible interfacing.
I've ben prepping some t-shirts to make my first t-shirt quilt, and after scouring this board, I went with Pellon 911. I had oodles of trouble getting the I/F to stick properly until I started using a wet press cloth. I think the steam gets between all the little fibers of the I/F and makes it adhere really well. It does feel a little stiff, but I think that it will soften up in the wash, like it usually does when I use it in clothing.
Also, I found it better to fuse a piece a little bigger that my intended block size, and then trimming it down made it much easier to work with.
Good Luck!