Love the idea, Kettle-- I use a sous vide to heat my stuff all the time -- I usually use mason jars, but I always toyed with the idea of using those bags for long-term soaks. Then you can freeze them in place for later work
I especially like the idea of letting cactus sit and heat for a day or two in my sous vide to really low-and-slow it. Same for caapi-- it is a great idea I think...
and TalkingGarden, you only have to make sure that the plastics you use are non-reactive to the chemicals in use-- much of it is perfectly safe you just need to check first.