As far as what rt to take, I would come in on I70 to exit 15B to 270 to exit 22B to 370 to your campground exit number 2, you will miss all of town so you will be golden.
If you are comming across IL on I64 I would take exit 7 to I255 to I270 so I could miss down town.
we live 2 hours from StLouis and go pretty often to The Sitemans Cancer reserch center, I have been to down town litterly 100's of times and have not been in a traffic jam in 15 years, they have alot of roads to take care of that if something comes up
Dar