This RinseKit Tailgate Shower is designed for pickup-truck-owning mountain bikers. It's a tailgate pad that features five molded EVA slots to hold bikes: And on the inside of the tailgate, it's got a 10-gallon bladder connected to a pump and hose. You plug the pump into your bed's 12V outlet or 4-pin trailer socket. You can then hose off your bikes (or yourself, if you're a cold-shower person) for, the company says, up to 16 minutes. The system runs $400, but you might want to go through some YouTube reviews by actual users (i.e. not influencers). Some have reported reliability issues with RinseKit products.