Hold onto them stainless, they not very commonly found these days last I heard. I have the stainless and beckett in mine and so if you should ever feel like getting rid of let me know
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Went through and redid my burner and insulation awhile back and even though I can say there really isn't all that much to a boiler I know the fabrication would take some time even if you have one to tempate it off. The hardest part to come by or to fabricate would be the inner chamber and outer skin end cap/donuts as they have lip going around each cyclinder.
If I were to make one I would design it as a verticle boiler building it up off castors. First I'd make an open frame angle iron box a couple feet square which both houses the burner/blower and supports the boiler above. One flat sheet of metal on top of square supports the burner below and gives surface to build the boiler above. Instead of the shiny outer cylindrical skin I might just go with red painted sheet like a hotsy maybe in a box shape. Since the design is portable and meant to be combined with small portable washer a power source is needed. Going dc blower/burner off a battery would be one way or if you want to stick with the 110 then you either stick an inverter in your vehicle or you stick an inverter/battery combo on the box itself. In fact I just stuck a 2500 watt inverter in my truck to be able to power various things...
Once in awhile portable propane whitco boilers do come up on Ebay..be easier that fer sure..
edit: I have seen steam box plans somewhere on the net..maybe delco..unsure..