My dad and I have been trying to rig modern hot tub plumbing through an old coal stove. So far, not so good. We coiled some copper tube in the stove to heat the water, but we've had a lot of leak issues between plastic plumbing and hot copper.
We have a couple of redwood tanks. They swell right up when you want to use them, or throw a little sawdust in to stop the last leaks.
I've been eyeballing the snorkel stoves for a while now.