I'll wholeheartedly endorse the garden sprayer/tea kettle method, after having used it for numerous years (full time) on a boat. Simple, effective, and portable - plus has other uses (spraying off muddy feet, pre-washing dishes, etc.)
I bought a dark green one to begin with, so have not painted it. On a boat, this lived strapped to the stern rail, so the water was often plenty hot; but if not, a dollop of hot from the kettle sorted it out.
You hand-pump the sprayer a few times to build up pressure, and then you get a great spray. In fact, the air pressure is really helpful in conserving fresh water because it kind of blows the soap off. You can get a really decent shower in very little water (if necessary).
The modifications I made were to take off the original hose and add a longer one, and to shorten the wand (others have replaced that with a kitchen sprayer or showerhead).
At the kitchen sink, I find the kettle to be completely sufficient. Heat up a little water and mix to suit. Virtually unbreakable and no added weight
. The water stays hot enough for dishes for quite some time, so the timing is not critical.
A thermos filled with hot water in the morning can be nice for mid-day if you don't want to heat water up again. Or add rice and have hot cooked rice ready when you arrive.
PS: Congrats on the Scamp!