  We provide a proof of global existence of solutions to quasilinear wave
equations satisfying the null condition in certain exterior domains. In
particular, our proof does not require estimation of the fundamental solution
for the free wave equation. We instead rely upon a class of Keel-Smith-Sogge
estimates for the perturbed wave equation. Using this, a notable simplification
is made as compared to previous works concerning wave equations in exterior
domains: one no longer needs to distinguish the scaling vector field from the
other admissible vector fields.
