A few times in the past I rode my DR650 up into the back of the truck. Though generally I would push it up one ramp while I walked up the other.
I do remember watching a guy getting fancy and riding his quad up the ramps and jumping it a little bit into the bed of the truck. He did this several times to the great enjoyment of his friends till on his 3rd or 4th jump he smashed right through the back windshield of his truck.
I have now have a very low van and its a breeze to load up a light 2stroke.