I lost my water tank heater element, it rusted through. I lost enough antifreeze to shut my truck down on a pour. Has anybody replaced one of these or is it even possible to replace?

Mine came from Arctic Fox. The one I had just screwed into the tank. A lot of good it did me, I still only have warm water in the summer time?

Mine's from Arctic Fox as well, I'm pretty sure it's stainless, and I know from looking on their site they do have stainless heaters.  Mine has always been great to me. 

http://www.arctic-fox.com/pdf/Electronic_Catalog_-B500_08-07_00.00.pdf

Well..I'm pretty sure it's not artic fox. Let me give some more info. 03 putz with a deck water tank that sits under the boom. It has a pipe inside of it that makes several turns on the bottom of the tank. It exits the front of the tank and connects via hose to the engine block for antifreeze circulation. I'm assuming this is a putz installed item. We did not put this on after market, it came with the truck brand new in 03. I only have 2 round access holes on top on of which the water pump is in.