  For five-dimensional braneworlds with an $S_1/\mathbb{Z}_2$ orbifold topology
for the extra dimension $x^5$, we discuss the validity of recent claims that a
gauge exists where the two boundary branes lie at fixed positions and the
metric satisfies $g_{\mu 5}=\partial_5 g_{55}=0$ where $\mu$ labels the
transverse dimensions. We focus on models where the bulk is empty apart from a
negative cosmological constant, which, in the case of cosmological symmetry,
implies the existence of a static frame with Schwarzschild-AdS geometry.
Considering the background case with the branes moving apart after a collision,
we show that such a gauge can be constructed perturbatively, expanding in
either the time after collision or the brane velocity. Finally we examine how
cosmological perturbations can be accommodated in such a gauge.
