You do need a dually tire gauge and likewise a dually inflation chuck. These have a sort of angled head on the end, with one port back at an angle (to get to the outer tire) and one forward on the end (for the inner tire). I find the style with the end port straight with the stem, rather than angled, is much more convenient.
With one of these and short valve extenders (1" or so) you should be able to check and air up the tires with only moderate hassle. The fancy extenders are nice, but you can get simple short airless ones that generally work fine too. Make sure your valve stems have a metal shank (as is usual for duallys) or are all metal; rubber valve stems with extenders tend not to last very well.
Dually tires can be rather a pain, truth be told. Ford's love for wheels with lots of tiny access holes doesn't help matters any.