I just finish my first tshirt attempt ever! I used simply sweet cartridge and vinyl. It isn't the greatest but I really enjoy doing it. I'll keep praticing until I get a neat result. I haven't try using the freezer paper it maybe easier and maybe I could get a solid line.
I did a test and it works well. I use a piece of cardstock & tape around the gel pen. I replace the blade housing with the gel pen. I did it only once and it works. I know it is pretty rudimentary & basic but it works for me.