Welcome to Mississippi! You won't find the summer heat any more pleasant, especially down there in Hattiesburg.
This thread is a great way to familiarize yourself with MS carry law, especially the first three posts. If you lose it for some reason, it's stickied at the top on the Mississippi sub-forum.
In short, open carry is legal without a permit, and concealed carry requires one. However, there's an opinion floating around that a firearm clearly visible and in a holster is partially concealed, therefore requiring a permit to carry. As ridiculous as it is, nobody seems to be willing to be a test case. Also, vehicle carry in any form is specifically protected without a permit.