A modular channel for a door including an elongated channel forming at least a portion of an internal frame for the door. The elongated channel has opposing sides and a base member extending between one edge of each side. The modular channel includes a pair of parallel slotted openings along the base member and a channel adapter including a tabs corresponding with the pair of slotted openings. The tabs include a locking protrusion extending from tab. The tabs slidably engage the slotted openings and the locking protrusions engage the slotted openings when the tabs are urged fully into the slotted opening. The slotted openings may be positioned parallel with the elongated channel length and the elongated channel may include at least one transverse slot perpendicular to the slotted openings. The channel adapter may include a curved locking tongue disposed perpendicular to the tabs and engagable with the transverse slot.