I tried BIAB for the first time a couple weeks ago, mashing in a brew pot on top of a stand alone propane burner.
Even with the burner on the lowest setting we had a hard time keeping it below 160F. Eventually we had to resort to turning the burner off all together for a while, then on for a while, and repeating that.
Another problem we had was measuring the temperature. The mash was a lot higher near the edge of the pot than it was in the middle, even though we stirred it almost constantly.