The I Could Do That in a Van is worth 20G and is unlocked by finishing the I Could Do That in a Van Rivals event having set a lap time of 10:00 or better.

Enter the Rivals menu and choose the "Spec Challenge" rivals set and then the "I Could Do That In A Van" event. You must be driving the Ford Transit SuperSportVan and get a lap time of 10:00 or less. You may use rewind as often as you would like without penalty. Run through it one time to see what your driving style ends up with for an initial time and see how much you need to trim to get under the requirement. This is primarily an exercise in nailing corners, so if you don't get at least a "Good Corner" rating, I would suggest rewinding.

The Ford Transit SSV is paid DLC that comes with the Car Pass. If you don't have the Car Pass, you can purchase the Top Gear Car Pack to get ten cars, or buy the Ford individually. Note that D280 is the highest rating the Ford can have and still qualify for the event. I would recommend weight reduction as the most important upgrade given that the Ford is a tank.