I'm about to try using a new Hamilton beach 22 qt roaster oven for the boil. Have had very good results using their 42 cup coffee urn for mashing (partial mash, 2.5 gal batch ), by the way. Heats up to mash temp quickly, can use the spigot to easily transfer the wort to the boil pot! The goal for the roaster is to get the wort up from ~150 degrees, to boil in record time. As for lower temp, I think it will do this without a problem. Will post results when I have them!
PS By the way, roaster & coffee urn on Amazon, very affordable!