Just an update. I'm still working on this and it gets more frustrating. SprinterAccessories.com says they no longer carry a receiver hitch to work on my 2005 Pleasure-Way Plateau B. They said they were out of stock and had no plans to add more now that the 2007 Sprinter van is out.
I could get off my duff and go visit some hitch places but have three camping trips planned and am trying to completely remodel our home kitchen before Thanksgiving. So I may wait until next season when the situation could get worse.
By then I might have to do a custom hitch receiver. Fortunately I know someone who could do it for me but he might do it in his specialty of welding stainless steel.