There are two types of A/C installation, The normal install the condensate just drips down on the roof and then runs off.. More on that in a second.
The other the water drips into a "Funnel" and from there is piped to the ground via a pipe or other type of "line" (Tubing) Or it can be dripped into a "Channel" that carries it to the edge of the roof (I am considering this, for later)
You can install a trim strip with a "J" channel on it that routes the water running off the roof to the front or rear of the RV, but frankly other than a major re-build (plumbing) that's about the only option.
NOTE: This is common on Flat Roof buildings as well.. And it causes all sorts of issues.