To be successful, you have to start at the bottom
To install a drawer bottom, you can rabbet the bottom edge of the front, sides, and back (before or after assembly) and glue in a panel, but that presents a potential weakness: Too much weight in the drawer could force the bottom panel out of the rabbet, spilling the contents. Instead, capture the bottom panel in grooves within the assembly. You can do this in several ways.
First, you can cut or rout full-length grooves [Photo A] on all parts prior to glue-up. With some joints (doweled rabbet, lock rabbet with integrated front and back), the joint itself hides the groove. But with pocket holes, box joints, and basic lock rabbets without an integrated front, the grooves will show (above right).
To avoid visible grooves in these joints, you can rout grooves on the router table. One method uses a box-slotting bit [Sources]. Simply dry-clamp the box together, then rout a groove by guiding the assembly against the bit’s bearing in a counterclockwise rotation [Photo B]. When finished, you have a groove with rounded corners, so round the corners of the bottom panel to match.
Another option: Rout stopped grooves prior to glue-up. Do this on the router table by securing stopblocks to the fence to stop the groove 1⁄4"–3⁄8" from the ends of the workpiece. With an upcut spiral bit installed and set to depth, position the workpiece against the right stop
[Photo C] and slowly lower the board onto the spinning bit, keeping a firm grip on the workpiece. Then slide the workpiece until it contacts the left stop [Photo D] and shut off the router. When it stops, lift the board to reveal the stopped groove. If you need a wider groove, move the fence back slightly and rout again, repeating until you have the desired width.