Personally, I agree with BobP. I don't think we can get the T shirt paint hot enough to truly heat set it, and change it's molecular structure, without ruining either the bait or the paint job, because we don't, as Ben pointed out, paint T shirts. We paint hard, porous surfaces.
If you put a plastic bait in a 325 degree oven for 20 minutes, I'm pretty sure it will burst from the expansion of the air inside it. I have not tried that particular experment.
Even with the PVC I use, if I heat it longer than a few seconds with the hair dryer on high, I get bubbling, either from trapped air, or from trapped solvent in the actual PVC material.
I use a hair dryer, first on low, and then on high, to drive out as much moisture as I can before I top coat, to avoid trapping moisture under the top coat.
Trapped moisture insures top coat failure.
I dip with a water borne urethane top coat, and heat set it, too, and the whole paint scheme is water proof when I'm done. I've had hook rash and rock "bites", but the paint scheme holds up.