I'd go to the Ford dealer and ask to look at a new dipstick and tube assembly. Some of the tubes use an O-ring seal to keep them from leaking.
Maybe that's your problem.
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.