We consider a system of mobile hard rods that are immersed in an isotropic matrix of hard rods with quenched positions and orientations. Using quenched-annealed density functional theory the disorder-averaged excess free energy functional is approximated by an Onsager second virial form, which is valid in the limit of large length-to-thickness aspect ratio of the particles. We find that inside the bulk isotropic matrices the isotropic-nematic phase transition occurs at higher values of the chemical potential than in the pure system, shifted proportionally to the product of the matrix density and the matrix-fluid excluded volume. We investigate adsorption and penetration behavior of the annealed rods at the planar surface of a porous rod matrix, considering both perpendicular and parallel boundary conditions of the nematic director far from the surface.