Problem simulating plastic part.

Hello,

I have a plastic part and I am trying to get an idea of its performance, but I faced several issues. I've attached the file and a picture of how it is assembled with the other parts. I am trying to simulate the board. It needs to hold 16" of water(3985.423N/m^2). Can someone suggest how exactly to fix it and ti apply the load? I've tried several configurations, but every time the simulation fails at the meshing. I need to do this. so I can make more rigid and lightweight design.

Thank you in advance and wish you all the best.