Unfortunately, I don't see how it wouldn't
get on the floor from the way yours is currently laid out. Do you use a shower curtain?
Our small wet bath has a "wall" & door between the cabinet & the riser of the toilet/wetbath. It keeps the water contained. The wood wall has a stainless steel panel on the interior to keep it dry. Maybe if you don't want a full-height wall a partial one would help...not sure. BTW, the design of ours was adapted from the original 1956
layout, the only variation in design we made was adding the tanks.
Maybe try tilting the trailer when you shower.
Yours looks nice though!
Where did you find the black toilet? Cool!