Except for long life durability (which the duct tape will probably not provide), the main difference is that aircraft fabric covering is pretensioned, traditionally using dope (which causes the cotton to shrink), today using heat (which causes the synthetic fibres to shrink). Hence aircraft covering is stiffer and does not "flutter" when subjected to airstream. There might be some significant stress on the covering if it is not kept under a certain tension, so it may fail after a very short time (like flags in the storm).