We started in 1998 when our boys were in pre- and grammar school. Although we didn't get out of Dodge for a year, we bugged out during every long weekend and for 3+ weeks in the summer. That was in a 30 foot Class C.
Beware of gutting and rebuilding an Airstream. My good friend bought one with the same idea in 2001 and its still sitting in his backyard. So you kindergartener may be in college before the camper is ready!
Your expenses could range from camping for free overnight at a Walmart to paying megabucks at Fort Wilderness. Just gas for a 30,000 mile year long trip would be $6000 to $9000 (10-15 mpg at $3 a gallon).
Go West young man!
Tom and Katharine
'07 Winnebago Tour 40TD, 400hp Cummins
RVing for 19 years & 150,000+ miles