Sorry to hear your issue. Seems that most all RV are thrown togther these days less you buy "second home on wheels" with a second mortgage to boot.
Noticed you took the screws out. If it works for you I would leave the screws out and seal the shower in with 4200 (3M marine) or a less agressive cailking, and then permenently seal the holes and cracks with some thing like 3M Marine Acryl-White Glazing Putty.
Once you get past the fact that it is broke and not build correctly just improve it and move to the next. There will always be a next....
Hoglou the DH & BK the DW (retired and happy)
WestGA KM4HQQ 146.640mhz
L'IL Foot" 2014 Sunseeker 2300
"Harry" the JK toad in the mirror
Check out the "mods" in the albums