Bath remodel options

[Nicholas Bronte]

Hi BP,

I have a duplex that I plan on using as a long-term rental.  There is a single bathroom in each unit.  In each bathroom there is what appears to be an older clawfoot tub that has been "built-in" with painted plywood or cement board.  There are no showers, likely due to the fact that the bathroom window prevents installation of a proper tile or prefab surround.  I have come up with the following options so far:

-install shower with glass block window with tile surround and bath vent fan (no idea as to how waterproof this may be)

-demo old tub, wall off window, install prefab tub/shower combo and bath vent fan 

-reframe window to be much smaller and higher on the wall, leave existing tub, install tile surround and plumbing for shower

-leave as is and hope tenants don't care about not having a shower

In most of these cases it seems to really just boil down to whether I want to have a window that can be opened to alleviate wet room moisture, or install a vent fan.  I'm kind of terrified of water penetration/damage in general.  Any opinions as to my current options, or new thoughts as to how to make your rental unit bathrooms bulletproof in terms of water damage would be appreciated.  Thanks!