There are at least two possible routes from St. Louis
to Seaside (Florida)
. One of them goes out I-64 and I24 to Nashville
and then takes I-65 down through Birmingham (Alabama)
If you stayed somewhere around Tanner
that would be about half way.
The other route, which I think I would prefer although it is a little longer goes through Memphis Jackson (Mississippi)
. Halfway would be about Winona (Mississippi)