Yeah Mark, you have two issues on some of these. The tendency for the polyester dyes to sublimate into light color inks at high dryer temps, and adding stretch for the ones with spandex.
The new silicone inks from NazDar are meant for just these issues, with lots of stretch as well as low curing temps built in. They are a little more involved, however with both higher pricing, and the need for a catalyst, and a limited mixed shelf life, so you will also charge more.
On small runs, I still often use heat seal materials. (Nylon, though rare, does require special ones)