  We consider skew products over subshifts of finite type in which the fibers
are copies of the real line, and we study their mixing properties with respect
to any infinite invariant measure given by the product of a Gibbs measure on
the base and Lebesgue measure on the fibers. Assuming that the system is
accessible, we prove a quantitative version of Krickeberg mixing for a class of
observables which is dense in the space of continuous functions vanishing at
infinity.
