Well, 100 kph is 62.5 mph, freeway speed, so a ragtop option is certainly practical. I'd certainly try to argue a gamemaster into allowing it. It beats getting your seats soaked. I hate soaked seats.
Soaked, or cooked (think in terms of old-school vinyl seats in Arizona summers). If I were refereeing, I'd assume at least a synthetic-canvas-analog top for the passenger section, if not the cargo bed as well.
Related: Do Vacc Suits (or other environmental suits) have self-clearing helmet visors? Try riding a motorcycle in the rain sometime...