I drive Tampa to Yuma 4 times a year (2 round trips). All the info provided is correct - especially the Mississippi River bridge being a PIA.
I am not sure if Gulf Shores is your half way point or only stop enroute. If this is your only planned stop then the following comments apply.
My first thought is I think you are a bit agressive on driving Orlando to Gulf Shores in 1 day. I usually drive Tampa to Pensacola on day 1 - though I could continue to drive but I stop around 4:00 PM.
Not sure where you are coming from in the Texas Hill country but - San Antonio and Houston are absolute nitemares to drive! Especially if you hit them in or near rush hour traffic. I always time it so the first city I hit will be around 6:00 AM which makes the second city around 10:00 AM. If you do hit trafiic - I think Gulf Shores is way to agressive in one day.
My most favorite rest stop in the U.S. is the Stenner Rest Stop on the Mississippi side of the Mississippi/Louisana state line. It has dump stations and wonderful parking for RV's.