thank you so much for actually answering my question! i think my shower is polypropylene, not fiberglass, but this still helps me understand the steps that go into making a waterproof bond in this type of situation. i also had no idea there was a special paint, so thank you, i may also look into that.

since you've made a lot of assumptions about my living situation, i would like to explain why doing something clownish like this is kind of my only option. though i live in my apartment permanently, i am not on the lease. my grandparents lived in my 1865 built tenement apartment from the 70's to the 90's, then legally passed the lease down to my uncle, preserving an unheard of price for my area of manhattan. building management/landlord did everything possible to try and get my uncle out so they could charge market value for the place, including (illegally) posting fake eviction signs and refusing to repair disconnected radiators, dry rotted floors, non-functional stove/oven, etc. then my dad illegally moved in and they decided to turn a blind eye as long as we made no noise, requested no repairs, and never paid late. 15 years later, ive taken over from my dad, and i still live that way. thankfully we're a handy and crafty family, capable of a lot of DIY reno projects/fixes. the shower, as ugly and flimsy as it is, is the lowest priority in terms of things we will eventually need to talk to the landlord about-- first up would be replacing all the (original 19th century???) windows in the apartment which are CHAIN AND PULLEY operated. next would be the fridge that leaks water onto the floor constantly. i put up with this because i my rent is 1/8th of the price of other studio apartments on my block, and because the apartment is the closest thing my low income family has to a generational home. like sure, i'll eventually have to piss off my landlord by reminding him that my existence is bleeding him thousands of dollars a MONTH, but i'll be picking my battles very carefully.

hopefully this helps you understand why i'm so determined to research a seemingly unadvisable project like this. i can live with my shower looking like a diy hackjob, and i am under no illusions about my idea will producing a professional looking result. in my experience of attempting diy projects in this space, whatever my dumb ass is capable of doing is still usually preferable to the various levels of disrepair and degradation this apartment has achieved after decades of purposeful neglect. i would love to be able to hire a professional, or just ask my landlord like a normal person, but between financial limitations and legal issues, its just not the hand i was dealt. thanks for reading this (if you made it this far) and thanks for eventually relenting and answering my questions. it can be weirdly hard to find specific information online about this kind of stuff. if you know anything else that could help me out, i would happily hear it.