  We examine the vertical component of surface area in the warped product of a
Euclidean interval and a fiber manifold with product density. We determine
general conditions under which vertical fibers minimize vertical surface area
among regions bounding the same volume and use these results to conclude that
in many such spaces vertical fibers are isoperimetric. Our main hypothesis is
that the surface area of a fiber be a convex function of the volume it bounds.
We apply our results in the specific case of $\mathbb{R}^{n}-\{0\}$ realized as
the warped product $(0,\infty)\times_{r}S^{n-1}$, providing many new examples
of densities where spheres about the origin are isoperimetric, including simple
densities with finite volume, simple densities that at the origin are neither
log-convex nor smooth, and non-simple densities. We also generalize the results
of Kolesnikov and Zhdanov on large balls in $\mathbb{R}^{n}$ with increasing
strictly log-convex simple density. We situate our work in relation to the
Log-Convex Density Conjecture of Rosales et al. and the recent work by Morgan,
Ritor\'e, and others on formulating a generalized log-convex density/stable
spheres conjecture.
