I agree with scarbowl. My boyfriend and I are both virgins too, and when we have sex, I do NOT want it to be in the backseat like most of our current excursions. Even if we have to rent a motel room, like scarbowl suggested.
PLEASE, for her sake, make it a tiny bit more romantic and memorable the first time. Afterward, mixing it up could be really fun for you guys, but the first time I think she's most likely to want romance, comfort, and memorability. It's hard to do sexual things when you're not on a bed (take it from someone who spends a lot of time trying to figure out how to do things in the backseat of the car).
:) Good luck! I hope you enjoy your wonderful experience!!