If you don't have the DLC yet you will need the Meyers Manx, one of the barn finds in the main game.
I did a drivetrain swap to all-wheel drive and then upgraded to A class, giving the vehicle plenty of power to make a jump. Should only cost 50,000-60,000 credits.
Then simply head to the first jump in the game - Rainforest Reveal Danger Sign - and get at least 300 FT on the jump. I detail the area at the beginning of the video.