Over the years there have been hundreds of shower stalls built using PVC tubing! And a Tarp or two ,A Simple design for any handy person ,but realistically a Garden a Hose with a decent nozzle and a couple of fatigue mats or pieces of same will work just fine ! Keep the bathing suits on ,or Not depending where We are and who We are with works fine!
Most RVs have an outside Shower ,but the garden Hose left in the Sunlight works as well!
Put a plastic wash pan outside the door to clean off the sand on their feet!