An assembly includes a first frame rail and a second frame rail elongated along a longitudinal axis and spaced from each other along a lateral axis. The assembly includes a crossbeam extending along the lateral axis and fixed under the first frame rail and the second frame rail. The assembly includes a first support member extending transversely from the crossbeam to a first end fixed to the first frame rail. The assembly includes a second support member extending transversely from the crossbeam to a second end fixed to the second frame rail.