I put a one-piece shower in for a customer. He'd bought it, it 'was just a bit bigger than the doorway".
Took off the door. Then the doorframe. Then part of the wall..... When we got it in the room, it turned out to be a bit bigger than the shower enclosure, so we had to move a wall there. But the floor was slated, and slates break easily....
DO NOT change it.

I like the decoupage idea. That is what Formica is, after all, and that is waterproof. Just paper, resin encapsulated.
As it's blue, perhaps fishes? Sandy floor, weeds up the wall? How can you get more twee than that?

Recolouring the gel-coat should be easy enough for someone like Bobert.