Rather than standing on the lift platform, try this
Coach Lift.
It's the fully engineered version of the Burr Industries screw platform lift, and has been installed (and easily removed) on hundreds of RVs around the world.
As for the toy hauler and scooters / powered wheelchairs, the ANSI standard is 1 foot of distance for every 1 inch of elevation. Based on that, you'd have to have a toy hauler ramp that's either about 18-20' high or hinged split in the middle! (DW is both a Certified Rehabilitation Counselor and a 30 year scooter user.)