Replace shower drain Thor Citation

Hi Guys,

I have been having problems with my shower drain.

This is for a Thor Citation 31UKS TT.

Upon inspection I noticed it is cracked.

I need to replace it.

First question: Does anyone know what the diameter is of travel trailer drains? Are they different than standard household drains and traps?
Are they standard sizes or do some come in different sizes?

The TT is at a campsite and I cant measure it currently.

Second question: This is in a corner shower. The only access I know of is through a small access door at the bottom of the shower stall. I anticipate this repair being problematic with such limited space. Any tips?

I considered cutting a hole in the bottom of the plastic membrane and working from underneath, but I'm not sure I want to cut into the underbelly.

Thanks,
iso