Great question and great line of thinking!
We’ve spoken with our contact at CfAT and he’s confirmed that there is a desire for a more Western approach to a shower with a showerhead. Currently when rangers are out on Country they wash using similar methods to the ones you’ve mentioned in your own experience, or in rivers and the sea using a plant-based ‘soap bush’, where the leaves lather up once they are scrunched in water, so there’s a desire for a more traditional mobile shower system.
I’ve linked below a couple of previous discussion forum posts to have a read of (if you haven’t already) which outline some considerations for your mobile shower design.
Again, great to see this line of thinking and I encourage you to continue to apply this critical lens throughout your design process.
Keep up the great work!