I don't have a RV garage, but my RV driveway/pad next to my house is about 110ft long and 13 feet wide from the road to the back of the pad. Truck and trailer is about 54 feet. I could have gone probably 30 feet shorter length and have been okay, but I wanted the trailer parked "behind" the house rather than right next to it.
It kind of depends on the street setup as well. I could have gone with a shorter length since I can use the neighbors driveway right across from mine if need be to maneuver. If I was limited to the street width, which is only like 12?ft that would make turning/backing/straightening the trailer with a short driveway more difficult.