Zodi used to make a unit that would work on top of the Westy stove. You may be able to find one used on eBay. Zodi has since come out with a new unit that requires a pretty good-sized stove to power it, IOW, not suitable for the Westy. I recall a number of people saying that they used them (the old model) with success. I suspect a lot depends on your expectation. One of the drawbacks to the Zodi units is when you turn the water off the heat does not shut off. So, when you go to turn the water back on it comes out scalding hot or you end up melting the hoses in absence of water. I suspect if you are just using this device for heating up some water for dishes it would be fine, but for regulated shower use I think this thing would be a source of frustration. 

The Coleman, despite its size, is still one of the best units I tried and can actually be used with 40� water from a stream or river for showers or dishes, without having to recirculate water to get it up to temp. 

Troy