may be to late but here is my suggestion:I have seen many travel w/ little ones. Mine are now older, 8, 10 and 16. But don't worry about using car seat. Your little one would go nutty sitting in it all day anyway.
The main safety concern we had: walking between cars can be very DANGEROUS! If it is bumpy, their little feet can get eaten up!
We usually team up. I walk through first. Hold door open. Then hubby send kids through to me.I grab them fast.
If you are worried and stilll want to use car seat, hook two or 3 belts together. Then wrap it around seat like a seat belt to hold.
If you can afford it, get a sleeper. They are great for kids!
Becki
PS we have done the Sunset to Disney World from Houston and back twice. Sunset to El Paso and also Cresent to New York from New Orleans. All fun!
This is a great experience for kids. Your little one will be to young to remember, so take lots of pics! And for the sake of others, try and keep kids contained, not screaming etc. I try and keep mine quiet, and hope that others do as well.