SWMBO has been on me for a long time to get a washer but I always avoid the issue by pointing out how they can't easily be retro fitted into my Jayco ensuite.
Maybe a couple of rubber mats on the floor of the shower cubicle might be the go. Heavy duty suction pads on the wall to tie it down & problem solved. Into the annex when staying for a few days perhaps.
Looks like a trip to Ray's Outdoor to check them out
Anybody thinking about those Companion Washing Machine,s at Rays Outdoors,best be quick there catalogue runs out very soon,not affiliated with rays just helping the gray nomads out.