Have you every caravanned together? Your four best friends might not end that way. Trying to decide on places and how long you stay might be difficult unless you all like to see and do the same things. Think this out carefully. I guess some folks would like this but we could never do it.
If you're traveling down an interstate and want to stop for one night enroute, you'll probably be able to do so without reservations but going to popular places, national parks, state parks, etc. it would be chancy for four big rigs.
Good luck!