We have finally given in and bought a washing machine. A very small one. It takes 1.5 kg at a time (about one double duvet cover), and can easily be picked up. It doesn't spin, so we are still interested in a small, cheap mangle.
It is however very practical. It fits in the fore-cabin hanging locker when not in use. It takes much less water than a big one, and it seems to get stuff pretty clean. Unless and until we find one which does spin, which we can wire and plumb in and will fit in what is currently the locker housing saucepans and the calorifier, it will do.
In the meantime, it fitted neatly on the back of our ever-useful folding bikes. We got some funny looks, cycling through Cartagena with a washing machine on a bicycle, but it worked for us!