How are most MH basement compartments made

So after trying to find how water got into my lower compartment in front of the rear tire

As long as I have had my MH which is a Thor water has "never" intruded into any of the bays. Taking into the fact she was also in 2 hurricanes with high wind and driving rain and no water in bays.

I'd also check for a water line leak.

When one of my water lines leaked it leaked into the bay compartment. Check the plex fittings. A very small leak over time adds up. And tighten the screws on the locks on the bays regularly.