80 foot drop in 285 feet of length. I have no standing water after a rain. My driveway is used for air brake system tests.

The 1/4" per foot slope is standard and in the length of our wheelbases we would have no trouble leveling the coach. While that might be the standard for plumbing I seriously doubt we would need anywhere near that slope on a driveway. If there is any concern about water flowing back into a garage just use a trench drain in front of the doors to catch anything that might enter.