We present numerical results on transport properties in quasi-one-dimensional (1D) double-chain systems in a magnetic field obtained by the use of the transfer-matrix technique. The two chains are coupled with bonds in random positions which mimic the topological disorder in the quasi-1D polymer system. There are two scattering mechanisms: the random positions of the interchain coupling and the random flux through the loops. We find that the former is suppressed by quantum interference if the interchain coupling at every link is formed by double-bond hopping, leading to the existence of extended states in the absence of a magnetic field. These states do not exist in the case of single-bond coupling. This difference between the two cases disappears in a strong field. The formula for the transmission coefficient is obtained from the numerical results in both cases.