Daniel,
This is what we use. Like alia176, we make the hot water in a pail, then use the 12 volt water/shower pump to take the shower. This baby puts out so much hot water so fast that you really can't use it direct, since it can make more hot water faster than you can haul more water in to replace what's used. So long as you have propane, you're good for all the hot showers you need.
That's also another reason to use the pail, instead of straight from the supply. Some folks like their hot showers so much they'd run through the entire supply. With the bucket, they know exactly what they have to shower with so need to get it done and rinsed before they hit the bottom of the bucket.
As for fragility, yeah, you don't want to fling it around, etc. But it will hold up to reasonably careful use. I built a small plywood box that our entire shower kit goes into. If it's protected from being packed in among other stuff, it should hold up for you.
BTW, I see there's a Reliance water/shower pump illustrated with another product. Those were no longer made when I put together our shower a couple of years ago, but I managed to find two for our needs. Unless they started making them again, you'll need to look for a suitable substitute, which will probably be more robust anyway. Ours are very serviceable, but as other illustrate you can put something like that together pretty easily.
