Originally Posted by Scotchmo
Try resting the tank on a wet towel. Or drape a wet towel over the areas that are already brazed. I have not tried that but it might work.
harbor freight has something called "hylo-cool" that i picked up for welding in new floorboards on my caddi' that i think would do the job for yah!
its a blue gel which dissipates when too hot so you know when you need more, I'd recommend covering the already brazed side, then running a strip about an inch to either side of area about to be brazed. this way it should absorb/shield most of the heat transfer!