How many of us are there? Owners of Dodge based RV's?

In Fords, with Dana axles, we're going to 75W-140 full synthetic. Walmart has the best price. Just be sure you get the FULL, since they carry it along with Dino and Blend.
On dino oil, a rather short change interval per Ford. On full syn, considered lubed for life unless submerged in water.
Early syn had some stability problems but with those resolved now, it's the way to go. Did our E450 with 9500-lb Dana, and our little Aerostar with 4.56 limited slip. All good.