I took delivery of a RT188P in June. On a fishing trip in July my boat sat out in a heavy evening rain. The next day I discovered water in ALL but one of my compartments. My front right compartment had an open plastic tote in it for wacky worm storage and had about a quarter cup in it. The right rear compartment had maybe a teaspoon. I emptied my boat and took it to the dealer for this issue along with a couple others. Their answer was to adjust the latches to close tighter. When I got the boat home I did a little test and still had water coming in. I decided to investigate and this is what I did and discovered.
I removed the gaskets from all of the compartments. The gasket is a "U" shaped channel with rubber hose attached to it. The channel has an aluminum core with a vinyl covering. When I removed the gasket I found the channel was expanded or widened in some areas. Being aluminum, I was able to pinch them back into shape. I put a bead of silicone in the channel and remounted them. When I remounted the gaskets, being sure to press them into the corners, some of them came up short...up to half an inch. Where the two ends of the gasket come together, there is a piece of plastic rod connecting the top hose section. Where the gasket came up short, I filled the gap with silicone. I did this to all the storage compartments that had a gasket.
The rear deck compartments are different, they do not have a gasket. They are basically a plastic tub with a lip. The only way the water can get in is through the latch. I removed the latch and found it to have three parts. There is the top part with the "T" latch that screws into a piece on the underside. There is a rubber gasket between the two pieces. I researched the latches and found they are most likely "Perko" T latches. They can be mounted over smooth or carpeted surfaces. Their installation instructions state the rubber gasket is NOT to be used over carpeted surfaces. All mine are installed over carpet. My fix was to cut away the carpet and reinstall with the rubber gasket. I had reservations installing over the carpet even without the gasket. I broke one of my latches trying to remove it and there is one I can't get off. It appears it was mounted when the carpet glue was still wet and had dripped into the edge.
So there are there are four ways water is getting into the compartments. Gasket not pressed into corners tightly, deformed gasket channel, the joint where the gasket ends meet, and the latch being mounted over carpet WITH the rubber gasket.
The inside of my stepbox was also wet. It appears the stepbox does not have it own bottom. It is mounted to the floor of the boat over the carpet and water migrates in. I'm looking for a piece of dry deck to keep items off the carpet in the stepbox.

Rained on me yesterday while fishing.....compartments are dry.