Ugly paint mural in need of removal on fiberglass**

If you are lucky it will go away with just rubbing..?

Is that on a fiberglass bulkhead or on a real sliding glass (safety) door or panel?
If it's fiberglass; I'd try plastic razor blades, oven cleaner, painters hand cleaner.
I had some bad luck with fiberglass paint remover, it did damage the gel finish. If you go there, pratice on small spots several times and I'd still keep the work area small.
Good luck.

+1 on the oven cleaner. Use the old original full strength Easy-Off heavy duty stuff. Forget the "fume free" low dose version as it won't work.

That's a Silverton so the wall is probably a formica veneer over plywood. You can remove the formica and replace it. If you do, thoroughly check the wood for moisture and replace while open. Those walls and the side triangles especially tend to wick up water that rots the non-marine grade wood.

Formica??
Plastic razor blade and a rum, maybe two....
I learned a long time ago, not much really sticks to formica, mostly just sits there.
Pressure washer should probably blow it away but capture the run off some how.

If there is a West Marine store or paint supply shop close, You would be amazed what those plastic razor blades can do. If it's really formica, you're done in minutes without a chemical slurry.

1. Sand.
2. Paint.
3. Admire Newly Painted Bulkhead.

If it is really formica, the fiberglas paint remover (gel / paste) will work,,, IF it's really formica...
If you're not 100% positive yet, keep up with what you're doing. Looks like some hardware in the bulkhead that may be an effort to finish around it. If a smooth surface can be found under the paint, may save some finishing time to keep striping.

I would just prime and paint it with Awlgrip or something else.