J.V.
Well, I don't want to "underalarm" you, but I think your trip will be just fine. We travelled with my daughter (at age 2) crosscountry 3000 miles travelling 8 hours a day and she was happy shaking a TicTac box watching all the unique scenery go by. Remember those days before videos? I think it is actually entertaining for the kids to look out the window and see some of the unique things. Granted freeways can be boring so having the video for a break in the monotony will help. I might suggest buying some little inexpensive baby books or little toys just to give her something unique to look at every hour or so. Other than that, I'm sure she'll be fine. As for naps, unless you plan on entertaining her for the whole trip, my guess is she'll fall asleep during part of it.
RELAX and enjoy your trip! Have fun!!