Number 1, I'd avoid Austin and come up US 281 then over to I-35 (for example at Lampassas. From Waco I'd take TX 31 to Tyler and TX 155 on to Linden and US 59 to Texarkana.
Nice camping at Tyler State Park or several good spots around Texarkana (example: Shady Pines.) From Texarkana no reason not to take I-30 to Little Rock and I-40 on to West Memphis, AR. Either Tom Sawyers or Memphis North KOA are good overnights.
I would take I-55 up through Arkansas rather than crossing over at Memphis. I-155 over to Dyersbury, TN and Union City and up to the Purchase Parkway in Kentucky. Lots of really good campgrounds in and around Land Between the Lakes. Kentucky Dam Village State Park and several really nice COE sites around the Lakes.
Take Western Parkway to Elizabethtown, KY and Blue Grass Parkway on to Lexington. Kentucky Horse Park is a nice campground near Lexington and one of the many nice place to visit in that beautiful area.
Someone has suggested Niagara Falls in Canada. I'd agree. You could take I-75 from Lexington to the Detroit Area. I'd go on up to Port Huron and cross over into Sarnia, Ontario. In fact I am going to do just that in June. We are staying in Fifty Point Conservation Area for the second time because we liked it so much. Easy drive over to Niagara Falls (we are going to stay a week and just drive over for a visit to the Falls.)
One could go on over to Montreal for a nice visit and I'm going to leave it at that-- Oh yes, there is Bar Harbor.
Just some ideas about the route.
