My current plan is to cut out and replace the rotted OSB just a 10x10" corner in the bottom of the hatch compartment and change out the marker side light that is just above the hatch. but i have fresh lapsealant on the roof and the vertical joint is pretty tight. Maybe the screws under the vinyl trim for the vertical corner piece?
The screws behind the vinyl trim as not high on the suspect list of a water infection point. That is not to say it cannot be, but it is less likely. Part of getting a water infection is about the odds and the conditions exposed to a potential leak. The screws are protected behind the vertical vinyl strip of the corner, and the bottom of the vinyl is not sealed totally so any water that made it down the molding and behind the vinyl would get out the bottom easier then wick in through a screw.
BUT, those corner screws do tell a story. By popping out the vinyl strip, start up high close to the roof and take a screw out and look at the threads. If they are pristine silver with no rust, then the wood they are screwed into is dry and odds are low a leak from up high is there. You can put the screw back in if it is good.
Then jump down about 8 to 12 inches and and remove another one. Check if it is pristine or starting to rust. Put it back in if pristine and move down another 8 to 12 inches and check another. Check all the way to the bottom of the wall. If you start to see a pattern of rust starting all the way to very rusted and goo on the threads, then a leak started up where the rust started and rot is underway were the goo is. The screws rust out most times from the inside out. Not the outside in on a camper as new as yours.
This pic (2004 T2475) shows the screw rusting from the threads on the inside. The corner in this case was wet from a roof leak, but a corner molding leak can look the same in the area where water was.
Here is another place to look. Since you have a wet cargo hole floor, the cargo door unit is suspect. It may be the foam seal is not tight sealing the door to the frame or it is leaking in between the door frame flange seal to the siding which is sealed with putty tape. Pull the vinyl screw strip off and look at the screw heads. If the heads have rust on them, take a screw out. If the screw is badly rusted, the wood behind has been wet and the putty tape seal can be suspect. See this cargo door that had a flange seal putty tape failure. The screw heads at the bottom are rusted from the threads on the inside.
Here is the other side of the camper cargo door with the same issue
Here is the damaged wood behind that cargo door
Since you have a slide camper, the rear wall is built to have a dam at the bottom below the floor. This dam feature will hold water and rot out the bottom of the back wall. Bad enough it can affect the camper floor above it.
Look at the bottom back wall sheet of siding by the bumper. That bottom piece of siding is held on with hex screws at the bottom. Look at the heads. If they are starting to rust, there is water behind that area. If the heads are white, take a few of those screws out near the wet cargo area and look at the threads. If they have started to rust, water is down in that wall dam area.
This picture is off of a non slide camper to show the screw at the rear wall I am talking about. This is a 2005 T2363 with a wet rear wall. The screw heads are rusting. While the non slides do not have the below floor dam area, a wet back wall can look the same on the outside.
Here is a slide camper (2006 T264SR) that had a left rear roof leak and a left wall corner leak. The water settled in the well below the floor. The camper floor is at the 2 x 4 height, the bottom of the well is at the bumper. Put you hand under the bumper and feel the black plastic at the bottom of the rear wall. If the plastic is mush, then the bottom board is rotted out. If the board behind that black plastic is rock hard, then odds exist water did not make it down there long ago. A moisture meter on the black plastic will tell for sure.
Those screw checks I mentioned above will help tell you where some of the water came in and where it may not have.
Using the moisture meter, you can scan inside the camper at the side wall and rear wall of the back of the camper and see if it is wet behind the wall board. And you can scan the floor to see how large the wet area is. You can scan the black plastic membrane on the bottom of the camper scanning up, to see if the insulation in the floor is wet and how big an area that it or the back wall is wet at the bottom. While inside the camper and in the closet next to the bed over the cargo door area scan the wallboard to see if it is wet, scan the side wall at and the rear wall, starting at the corner and working outward, ceiling to the bottom of the cabinet which is the top of the pass through cargo hole.
The ideal need is, before taking the camper apart, check all the areas around the wet wood you found. How did it get wet? A leak from up high, a leak from getting in the corner molding, a leak getting in from the cargo door flange, a leak at the clearance light other areas?
You really want to find "all" the leak sources and figure out how to address each of them so when you do your fix so water will not be getting in to damage your new repair. Most times you can find more than one smoking gun leak, there generally are several.
Take pic's and post to of the suspect areas, and the roof corner. They can tell a lot we and you do not often see.
Hope this helps
John
