  We investigate the one-dimensional Kondo lattice model (1D KLM) for
ferromagnetic Kondo couplings. The so-called ferromagnetic 2-leg spin ladder
and the S=1 antiferromagnet occur as new one-dimensional Kondo insulators. Both
exhibit a spin gap. But, in contrast to the strong coupling limit, the Haldane
state which characterizes the 2-leg spin ladder Kondo insulator cannot fight
against very weak exterior perturbations. First, by using standard bosonization
techniques, we prove that an antiferromagnetic ground state occurs by doping
with few holes; it is characterized by a form factor of the spin-spin
correlation functions which exhibits two structures respectively at $q=\pi$ and
$q=2k_F$. Second, we prove precisely by using renormalization group methods
that the Anderson-localization inevitably takes place in that weak-coupling
Haldane system, by the introduction of quenched randomness; the spin-fixed
point rather corresponds to a ``glass'' state. Finally, a weak-coupling
``analogue'' of the S=1 antiferromagnet Kondo insulator is proposed; we show
that the transition into the Anderson-localization state may be avoided in that
unusual weak-coupling Haldane system.
