A rig mat frame has at least two longitudinal frame members and at least two lateral frame members defining a deck insert opening therebetween. Each longitudinal frame member has a C-shaped channel facing the deck insert opening and extending along the length of the longitudinal frame member. At least one C-shaped channel has a longitudinally extending flange with a channel opening providing access into the C-shaped channel. A flange panel is removably fastened to the frame and closes the channel opening when the flange panel is fastened to the frame. A plurality of deck inserts are disposed within the frame and extend across the deck insert opening with the ends of each deck insert disposed in the C-shaped channels. And each of the plurality of deck inserts is removable from the C-shaped channels when the deck insert is positioned in alignment with the channel opening and the flange panel is disconnected from the frame.