Never encountered the need to do this, but reading your description, I'd start with this. Drawing the picture I have in my mind would make it easier, let me try describing ...
(1) Measure the vertical rise at the rear wheel of proposed trailer, until you intersect the horizontal plane where the bumper or lowest portion of your trailer would potentially hit the driveway.
(2) Measure the horizontal distance between your vertical line at the wheel and point of contact.
(3) You now have a right angle. At the start of the driveway, measure the vertical distance, and horizontal distance to see if you hit the pavement before you get your full distance measured.
Follow my thinking? Let's see if others have done this, how close I am to something that works.