If you don't try to reheat the mash, you won't scorch your grain bag. And if you heat the water to strike temperature, stir in your grain, turn your burner off, and insulate the kettle a bit you shouldn't need to reheat it unless you're brewing in extremely cold temperatures.
I bought a vegetable strainer originally to keep the bag off the bottom of the pot, but now I don't even bother using it.
Their was an article on one of the brewing magazines that trying to reheat a mash in BIAB wasn't very workable because of the physics of thermal mass.
If you like the BIAB process, buy or make another bag and just make sure you don't try to heat the bag with grain in it.