hearing more on your philosophy, I think that if there's any way you can include the kid in the process of pedaling across the country, as compared to being a passenger the whole way... you really should. Think of what it would do for your daughter to help out!! Either a stoker/tandem set up, or a tag along. Think of what a learning experience it would be to be a particiapnt and contributor for her. Keep the trailer for gear, and for when she gets tuckered out. Also, being on the bike with a parent will be much less lonely than being in a trailer. think of the conversations you can have, the hands on learning about talking about what you see, as she is right there.
just 2¢ of course

Irulan