1997 Dutchmen Roof Problem

[dean320]

Hello, this is my first post here.  I just bought our first popup, a used 1997 Dutchmen.  The previous owner (a coworker I trust) said it never leaked on them and pointed out that the only issue was the front left corner (where roof, left side and front come together) where the original caulk gave up and it was redone.  He said I should probably recaulk it.  

Tonight I scraped off the old caulk to apply new and noticed that the corner trim had pulled away and that moisture had gotten in.  All of the screws turned freely so I knew there was damage.  

How do I fix this?  My neighbor, who frames houses, suggested removing the whole side, getting in and removing the moist areas, put plywood or 1x2's in, securing them through the top with screws and then screwing the corner trim pieces into those.  

Is that a good idea or can someone here suggest something better?

Thanks in advance for any assistance.