Most people who are liveaboards in urban areas live at
marinas with showers and
laundry, and use the marina shower even if they have one on the boat. Less to clean, less humidity, less fuss.
Adding a shower to a boat that does not have one designed in could take some
work. If it has a separate
head you could put a drain in the floor with a sump
pump and a shower faucet off the sink.
Easiest is to add one in the
cockpit where the
water just drains out.
To put it in perspective I've lived aboard for six years, have a separate shower stall and a
cockpit shower and I can count the times on one hand that I've used the stall. But it makes fabulous
storage space.