Do you have the part number for the unit you have? It should be on the top on a sticker or available from Jon Brazel. That will give you a place to start. They are rather pricey. I remember having to look extensively for mine, and eventually found it on eBay. There are a lot of different part numbers. It was never clear to me if there were big difference from one to another, but there is a risk to just put any pump in there. Monkeying that tank around is no fun, is it?
2004 Tiffin Allegro 27.5 ft. P32 18,000 lb GVW. 8.1 liter. Workhorse chassis built May 2002. 24,500 miles. 2012 Jeep Liberty Toad. RVi2 brake unit.