Ouch! Got the quote from Monaco - $276! They also had this to say about accessibility:
As for accessing the sending unit, usually it is on one side or the other of the fuel tank (rarely in the middle). The panel where the fuel port is located is most likely a false bay door, look along the side or underneath for screws holding the panel in place, once these are removed then it should hinge out like a bay door.
I also called Sales at Centroid. They don't stock the exact replacement, but will build one for you. She said you may be able to see the part number on top - if not you may need to pull it out to find the part number. As a last resort, they will ask you to take it out and measure it. She did not give a price.
She is not able to sell directly to me in FL, but I would need to contact either Alliance Coach or Lazy Days. If I don't like their price, I can always have them ship it to TX and I can get it when I fly there for Christmas later this year.