Bed slide "flange" problems

The bed slide trim on my Greystone Re32 slide is flexing inward when the slide is out. Just looking at it it looks like the slide is a box and 1/2 plywood flanges were fastened to the box to keep it from falling out of the trailer. This seems to be a normal set up but my main slides seem to have some bracing and this does not. The trim is a 1x6 trim boards with separate corner blocks. The flanges have flexed so much that the blocks have came loose. It is all wrapped in rubber fabric so I can't see much. Does anyone know how this is put together? Is there a brace somewhere that keeps the flange solid or is it just nailed/screwed to the "box"? I'd send pictures if I could figure out how. Thanks, Jeff

It is a Heartland brand. Like a Sundance only Gray. Made only a couple of years.