Sea Ray

I had the same problem. It is shower/Ac sump.

That compartment has no connection to the shower sump area. I had water in there as well. The two places I traced as possibilities were the drain hose from aft shower leaking or from an overflow of the drip pan in the main salon A/C unit. For my case it came from the A/C drain pan that the drain clogged and overflowed.

My Sea Ray in a 1998 Sundancer. I had a similar eater issue and it was my fresh water storage tank was leaking. After much effort to find the source, if I had it again, I would remove the table in the rear stateroom and then the foam in able to get to the bottom of the boat and vacuum it out. if you are getting water there, it is your plastic water tank. Had one made and replaced the old one.

Main salon A/C drain pan plugged and overflowed.

I had my shower mixer in forward head leaking until I found that the rigid water lines are installed at such a severe angle at the connection that they were bound to lead eventually.