It might be an orphaned product. Trademarkia says the trademark is "dead"; i.e., the owner let it lapse. Also, I can't find Hideaway Products in a Google search.
I'd call Tiffin Parts to see if they have replacement bags.
If the company is defunct, the product is orphaned, and Tiffin has no source for the bags, you might consider the Dirt Devil central vacuum. We have one in our '06 Bus, it works well, and bags are widely available. Installation won't be hard, and it will probably cost less than your next fuel stop.
1976 Southwind 28', '96 Winnie 34WK,
2006 Tiffin Allegro Bus 40QDP