I have been doing partial mash BIAB in a 5G stainless stock pot.
I tried mashing on the stove with limited success. Every 20 minutes, I'd stir, check temperatures, and fire up the burner to bring the mash back up to temperature. I found the temperature dropped too quickly. Perhaps if the burner was turned down low enough, and the mash stirred often enough, the proper mash temperature could be maintained throughout, but I never tried this.
Then I tried wrapping the pot with a sleeping bag. That made it harder to check the temperature of the mash, and really difficult to use the stove to heat the mash back up to the desired temperature. While it held temperature much better than being in the open air on my stovetop, the mash temperature still dropped more than I was comfortable with.
Then I tried using my oven. Even though my oven's thermostat only goes down to 170 and has quite a wide delta between shutting off and turning back on, it held my mash to the desired 152 degrees quite well. I still, every 20 minutes, remove the pot, stir and check the temperature, and return the pot to the stove, but this seems to work the best of all the methods I've tried.
I've just recently converted an insulated water cooler into a mash tun, so I'm hoping I'll no longer need the oven for mashing.