Showers are a selling point in many a nomadic home. Unfortunately they all to often degrade the nomadic home, more than they enhance it. There are two main reasons that a shower can degrade a nomadic home. They are either to small to be practical to use and/or they are put it in the same space as the toilet, which makes everything (including the toilet paper) wet. In either scenario, I think you are better off without the shower, and should find another way to wash.
If you feel that you have enough room to install a shower, I believe that you need a minimum base of 24X32 inches (600X800mm). You can fudge these numbers a little, if you use a triangular shape, but you still need a cross section of about 32 inches (800mm) minimum.
When it comes to the plumbing, you can go to town with electric pumps and hot water califonts. Personally I prefer a more low tech solution, which can give just as good a shower.
Having grown up on the briny ocean. I know only to well, just how quickly the sea air destroys just about anything, especially if it has metal, moving parts, or relies on electricity. So for the low cost, low tech, low pressure solution, I would go with a plastic solar shower. Just heat your water to the desired temperature on the cooking stove, fill the shower and use. Or even better, if you want more pressure, while retaining low cost, low tech, then a six litre (1.5 USGal approx) garden pressure sprayer. Again heating the water to the desired temperature, on the cooking stove. Fit a shower head to the end of the hose, give a few pumps and you have a cheap, efficient, reliable shower.
Alternatively, if you don’t have enough space to fit a shower inside your nomadic home, you can mount a shower curtain on a three foot (900mm) diameter hoop and attach it to either a tree, the mast on deck, or the back of your mobile home. Then use either the solar shower or garden sprayer.
While it’s not a method of washing that I am an expert in. I have it on good authority that a sponge bath with a cloth of just the right size and texture is a sybaritic luxury in at least the same class as a good shower, requiring much less plumbing and water.