Probably your best bet would to get the 2" drop stinger, this will give you the maxium of road clearance possible. If you are still too low then turn the 2" drop stinger over (it then becomes a 3/4 rise I think) and put the ball on the high side.
Somewhere in that range you should be able to find something close. If you are really particular on this most larger RV shops have a wider selection of hitch balls of varying heights that are used to make up smaller differences after you get close with the stinger height. This link will give you an idea of the variety of ball heights
I personally prefer a very slight nose down attitude on the trailer after the rig and trailer are fully loaded to travel.