Assessing water damage

[ports]

I am trying to find out how to assess some water damage I noticed.  I'm not good with taking pics and posting so I will do my best explaining.  If you can picture outside the cab where you enter the vehicle, ( where you have to duck or wack your head) that horizontal stretch of the overhead cab.  I check the caulking there every year and re- caulk.  I recently noticed that the bottom in a 1 foot section had lowered or pulled away from the right angle piece at the bottom. I could push that small section up.  Along the rest of the overcab, it was solid.  When going inside the motorhome and looking at that area from inside, I noticed that there was a soft spot on the floor or base( not on the side) which coincided with what I observed outside. I pushed along the side of the motorhome above the base and it was solid.  I have not seen any type of water stain anywhere on the ceiling, front, or sides of the overcab.  The passenger side of the overcab inside and outside is good.  It appears to me to be a small section along the base of the plywood bed where damage has occurred.  My main question is what do I have to do to be able to access the damaged area to fix it.  There is a vinyl skin on the top of the bed.  I know it is difficult for you to comment when I have no pics.  I guess what I need to know is how to remove the vinyl where it is soft.  I'm hoping that if I can access that I can replace a small section of plywood and re-caulk.  Any suggestions would be very helpful.  I have searched this site for help and have seen cab rebuilds but nothing on how to start.  Everything was already ripped apart.  When I Googled this, the same thing.  All projects were already exposed and just showed everything being ripped up and replaced.  When I bought my 1994 Winnebago Micro Warrior, it was well taken care of over the years by the owner so I do not believe that there is any type of extensive damage. I hope I did not confuse you with my description.  Thanks for your help and expertise.  Ports