Cross Country Trip - What length Class C???

I will second a few other posts. How many are making the trip with you. There are advantages to the different sizes. Short rigs have more CCC and it is easier to find parking when playing tourist. The wife and I have a 26.5' rig that is just right for us. I do a lot of longer solo trips (I am retired, she is not). I have not had trouble finding parking in campsites, but at sight seeing stops along the way even this length is sometimes long.
Also look at the amount of overhang. As already mentioned there is a ratio of length to wheel base that makes a big difference in handling.