I suppose that since you're in SE Michigan it's much closer to take I-75 all the way. Being in SW Michigan (and looking for a flatter route) we take I-69 down to Indianapolis then I-65 into KY-TN-& AL until Montgomery, AL where we catch US231 down to I-10. We head east on I-10 to Florida exit #225 where we head south on US27/US19 to Crystal River, FL where we stay.
If you're going into north central FL you can either stay on I-10 until I-75 or take the 27/19 route down to Chiefland, FL where you'd catch US27 over to Ocala.
I've driven I-75 all the way from Gaylord, MI (used to live there) in a car to Tampa and I recall telling my wife that I really didn't want to take that route with our camper. The elevations in the winter months with any precipitation doesn't make for carefree driving in my opinion. I've driven in snow all my life, but once you get into KY or TN they just don't condition the roads adequately in wintery weather.
As far as camping along that route we usually stay the first night in a motel (around Bowling Green, KY to Nashville, TN) and then the next night in a campground in AL. There's a very nice one just north of Troy, AL called Deer Run. It's got FHU's with cable for under $30 with Good Sam. From there it's only 350 miles to Crystal River and about that to Ocala.