I've been furtling around in the cellars at Haymarket Towers and found a post from Steve in Leo on this subject from 9th March 2008.
Steve wrote:
'I have used the two spaced ramp method for the last ten years. Having measured the distance center to center of the axle spacing on our twin axle van, I now set the ramps out at 41 inches apart from peak to peak. This gives excellent levelling results in the dry. To aid our winter caravanning, I have screwed the ramps to 65 inch length of builders plank. This holds the ramps firm and stops any sinking and damage on grass pitches. I also have a plain plank the same length (65 inches) to go under the other side to stop the wheels sinking. For storage on the van, I have fitted a steel "u" shaped loop just behind the back axle, to both chasis rails. I slide the ramps accross the van through the loops and secure the ends with a "G" clamp at each end to stop them sliding out. A little bit of forward thinking saves a lot of struggling in thewet and windy winter. Hope you have lots of fun. Steve L.'
Personally I line the caravan up with where it is to be pitched, align the levelling ramps with the wheels that need to be raised at the side, reverse back, move the ramps across to line up with the axle track and drive slowly forwards. The front caravan wheel rides over the rearmost ramp and begins to climb the second by which time the rear caravan wheel is climbing the rear ramp.
When the caravan is level I apply the car and caravan handbrakes, place the anti rollback chocks behind the raised caravan wheels and unhitch/ lower the corner steadies.