My thoughts on RV aero include tackling the many protrusions that likely contribute to drag all out of proportion to their relatively small size, like roof a/c, roof racks and pods, that yuge canopy on the side, giant mirrors-on-a-stick, various antennae, and so on. Do some soul searching and decide if deletes are something you wouldn't mind?
The aero tail as Charlie mentioned should be an effective mod, perhaps the best one of all. Air dam could help too.
Non-aero thought: weight. Or more specifically, weight reduction. I've been to enough camper ralleys to know that many people pack
everything including the kitchen sink. I think travelling light could only help. Things like, do we really want to fill the water tank when the destination has showers and whatnot? Lots of weight there.