If the wall mount is standard , once the floor ( deck ) is attached to the frame the walls are stood onto the deck , the wall outside lip overhangs the deck, while the main load of the wall is supported on the deck , and the wall is attached with screws to the deck's outside edge , through the rail along the lower edge, the attaching screws are then covered with at vinyl strip.
If you remove the vinyl strip ( it'll probably fall apart ) they're only good for a few years , the screws will become visible.
This end on photo shows the vinyl ( black ) installed in the rail ( molding ) screws are center so the vinyl curves over them .
EDIT: I just noticed; after blowing up several of your pictures ; that the end caps of your trailer are attached the way I've described , but the side wall doesn't look to have the same molding. I'll see if I can find any info, on your attachment ( wall to deck).
Re-edit : after blowing up all your pictures , I'm seeing , other issues , daylight visible under the front wall across the floor; picture 3 ; and bulging on the front wall where it crosses the frame ; pictures 1&2. Check out all areas of possible water damage , to get a feeling of the full extent of the needed repairs, this may prove to be a can of worms.
99DSDP 3884, Freightliner, XC, CAT 3126B, 300 HP /ALLISON 3060
2000 Caravan toad, Remco & Blue Ox.