I would start by avoiding I-75 in Florida too.
I set my GPS for "no highways" on a recent trip from Ocala to Tallagega and it picked a good route; mostly 4 lane roads, not a LOT of little towns and very little traffic.
If you have a GPS try it and see where it wants you to go.
You can do that with things like Mapquest and GoogleMaps too where it is easier to see the whole route.
Only two situations where that is not good, in my opinion:
BIG towns. Not taking an Interstate is a big mistake and can take FOREVER.
MOUNTAINS. Not taking an Interstate can put you in a bad situation with an RV. Steep grades, narrow winding roads are not fun in an RV.
And lastly, sometimes an Interstate is the only good choice......like going N/S through Missouri and Iowa. IF the Interstate is not a part of a major route across multiple states (like many of the E-W ones are) the traffic shouldn't be nearly as bad.
