Couldnt be simpler.
Any shaped cutter will work. If your box is dead square then just adjust the fence as far away from the wood as the cutter needs. If the box is curved or shaped then you need a bottom bearing guided cutter.
Remember that a router table has everything upside down. So a bottom bearing, once in a table, is now a top bearing. Turn your wood upside down, adjust the bearing so it tracks firmly along the bottom edge of the wood, and just run it along.
Practice on scrap, it needs a steady speed to stop the wood from burning in places.
Any shaped cutter will work. If your box is dead square then just adjust the fence as far away from the wood as the cutter needs. If the box is curved or shaped then you need a bottom bearing guided cutter.
Remember that a router table has everything upside down. So a bottom bearing, once in a table, is now a top bearing. Turn your wood upside down, adjust the bearing so it tracks firmly along the bottom edge of the wood, and just run it along.
Practice on scrap, it needs a steady speed to stop the wood from burning in places.